SPARK series / Capstone
The SPARK Interview Workbook: 100 Coding Interview Problems That Train Pattern Recognition Instead of Memorization
A reasoning-first workbook with 100 coding interview prompts that train signals, properties, assumptions, pattern choice, rejected alternatives, and interview communication before implementation.
Workbook
100 reasoning-first problems
Core skill
Pattern recognition
Reader mode
Think before coding
Final goal
Interview-ready judgment
Before the problem list
Start With the Interviewer Question
Most candidates do not fail interviews because they have never seen code before. They fail because they commit too early. They see subarray and say Sliding Window. They see sorted and say Binary Search. They see tree and say DFS. Experienced interviewers listen for a different skill: can you explain why a pattern fits, what assumption makes it valid, and what would make you switch? This workbook turns that skill into deliberate practice.
Interviewers are testing whether you can reason under ambiguity, reject tempting patterns, verify assumptions, and communicate a defensible path before coding.
How to use this workbook without turning it into memorization
This capstone is a workbook, not a catalog of solutions. The point is to slow down before code. For every problem, first identify the signals, translate them into properties, list candidate patterns, verify assumptions, choose a pattern, name supporting data structures, reject weaker alternatives, and then explain the decision like you are speaking to an interviewer. A few later-series topics such as Dynamic Programming and Backtracking appear in the workbook because real interviews mix them. Their dedicated deep-dive articles are not assumed here. Treat those entries as capstone practice prompts that test whether you can recognize repeated subproblems or exhaustive choice-building when they appear.
The worksheet you should use for every problem
Use the same worksheet every time: Signals, Properties, Candidate Patterns, Verify Assumptions, Chosen Pattern, Supporting Data Structures, Interview Justification, Complexity, and Reflection. The order matters. Candidate patterns come before commitment. Assumptions come before implementation. Reflection comes after the answer so you notice what almost fooled you. This is how you train pattern recognition. You are not trying to remember that a named problem belongs to a named algorithm. You are learning to reconstruct the right decision from the prompt.
Difficulty progression
The workbook moves through five sections. Foundation problems build confidence with obvious pattern signals. Intermediate problems introduce ambiguity and ask you to eliminate reasonable alternatives. Hybrid problems combine a primary pattern with a supporting data structure. Interview traps deliberately use misleading keywords. Senior-level problems ask for trade-offs, scalability, maintainability, and requirement changes. This structure mirrors real interview growth. Early practice asks can you recognize the pattern. Later practice asks can you defend it under pressure.
Pattern comparison matrix
Sliding Window means a live contiguous region. Two Pointers means relationships between positions. HashMap means memory and lookup. DFS and BFS mean traversal shape. Binary Search means ordered elimination. Prefix Sum means cumulative reuse. Heap means dynamic priority. Dynamic Programming means reusable subproblems. Backtracking means exploring choices with undo. The strongest candidates do not memorize 100 separate answers. They learn these properties and map prompts back to them.
Real-world read
This is like choosing between an index, queue, cache, scheduler, or traversal in a production system. The tool follows the property.
Judgment call
Pattern names are shortcuts. Properties are the source of correctness.
Say it like this
“I am choosing the pattern because of the property, not because of the keyword.”
“The rejected pattern fails because one of its assumptions does not hold.”
How senior engineers think during coding interviews
Great candidates rarely memorize hundreds of solutions. They observe signals, identify properties, generate candidate patterns, verify assumptions, defend their reasoning, and then implement confidently. They also know when to change course. If negative numbers break Sliding Window, they pivot. If sorted data asks for a pair, they consider Two Pointers instead of blindly using Binary Search. If Top K appears after frequency counting, they combine HashMap and Heap. Interview success doesn't come from remembering every solution. It comes from consistently recognizing the right pattern, explaining why it fits, rejecting weaker alternatives, and then translating that reasoning into clean, correct code.
Real-world read
The best interview answers feel like calm engineering judgment: here is what I see, here is what it implies, here is what I reject, and here is the simplest correct path.
Judgment call
Reasoning does not replace implementation. It makes implementation focused and defensible.
Say it like this
“Here is the property that drives my choice.”
“Here is the assumption that would make me change patterns.”
Reason before solving
100-Problem SPARK Interview Workbook
Use this before every problem
The SPARK Attempt Flow
Do not open the answer first. Work through these steps, say your one-minute justification out loud, then compare it with the interviewer review.
Find Signals
Underline words like sorted, subarray, range, tree, Top K, target, duplicate, or stream.
Map Properties
Translate signals into facts: contiguity, ordering, hierarchy, lookup, cumulative reuse, priority, or repeated choices.
List Patterns
Write every reasonable candidate before choosing: Sliding Window, Two Pointers, HashMap, DFS/BFS, Binary Search, Prefix Sum, Heap, DP, or Backtracking.
Verify Assumptions
Check the constraint that makes each pattern valid: positives, sorted order, monotonicity, static input, visited state, or K size.
Choose and Defend
Pick the strongest pattern, name the supporting data structure, reject weaker alternatives, then discuss complexity.
Problem promptFoundation Problem 1: Maximum Average Subarray of Size K. Given an array, find the maximum average of any contiguous subarray of size K.
Interviewer review
Reader Worksheet
Signals
fixed K, contiguous, average.
Properties
one moving range with predictable add/remove updates.
Candidate Patterns
Sliding Window, Prefix Sum, brute force.
Verify Assumptions
K is fixed and the window moves one step at a time.
Chosen Pattern
Sliding Window.
Supporting Data Structures
None.
Interview Justification
I would choose Sliding Window because one moving range with predictable add/remove updates. I would not choose Prefix Sum is possible but heavier for one moving window because it does not match the property as directly.
Complexity
O(n) time, O(1) space.
Reflection
The tempting shortcut is committing from the keyword instead of proving that Sliding Window fits..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Prefix Sum is possible but heavier for one moving window
- 4.candidate refines by defending Sliding Window
- 5.expert feedback: Strong if the candidate names the property before implementation..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptFoundation Problem 2: Longest Substring Without Repeating Characters. Find the length of the longest substring without repeated characters.
Interviewer review
Reader Worksheet
Signals
substring, longest, no repeats.
Properties
variable contiguous region with validity state.
Candidate Patterns
Sliding Window, HashMap, brute force.
Verify Assumptions
Removing from the left restores validity.
Chosen Pattern
Sliding Window.
Supporting Data Structures
HashSet or HashMap.
Interview Justification
I would choose Sliding Window because variable contiguous region with validity state. I would not choose Brute force repeats work because it does not match the property as directly.
Complexity
O(n) time, O(k) space.
Reflection
The tempting shortcut is committing from the keyword instead of proving that Sliding Window fits..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Brute force repeats work
- 4.candidate refines by defending Sliding Window
- 5.expert feedback: Strong if the candidate names the property before implementation..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptFoundation Problem 3: Two Sum. Return indices of two values that add to target.
Interviewer review
Reader Worksheet
Signals
pair, target, indices.
Properties
complement lookup, not contiguous.
Candidate Patterns
HashMap, sorting, brute force.
Verify Assumptions
Extra memory is allowed.
Chosen Pattern
HashMap lookup.
Supporting Data Structures
HashMap value to index.
Interview Justification
I would choose HashMap lookup because complement lookup, not contiguous. I would not choose Two Pointers may lose original index after sorting because it does not match the property as directly.
Complexity
O(n) time, O(n) space.
Reflection
The tempting shortcut is committing from the keyword instead of proving that HashMap lookup fits..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Two Pointers may lose original index after sorting
- 4.candidate refines by defending HashMap lookup
- 5.expert feedback: Strong if the candidate names the property before implementation..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptFoundation Problem 4: Two Sum II. Find a target pair in a sorted array.
Interviewer review
Reader Worksheet
Signals
sorted, pair, target.
Properties
ordered pair relationship.
Candidate Patterns
Two Pointers, Binary Search, HashMap.
Verify Assumptions
Array is sorted.
Chosen Pattern
Two Pointers.
Supporting Data Structures
None.
Interview Justification
I would choose Two Pointers because ordered pair relationship. I would not choose HashMap ignores sorted order because it does not match the property as directly.
Complexity
O(n) time, O(1) space.
Reflection
The tempting shortcut is committing from the keyword instead of proving that Two Pointers fits..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with HashMap ignores sorted order
- 4.candidate refines by defending Two Pointers
- 5.expert feedback: Strong if the candidate names the property before implementation..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptFoundation Problem 5: Search Insert Position. Return where a target belongs in a sorted array.
Interviewer review
Reader Worksheet
Signals
sorted, insert position.
Properties
ordered boundary.
Candidate Patterns
Binary Search, linear scan.
Verify Assumptions
Array ordering is reliable.
Chosen Pattern
Binary Search.
Supporting Data Structures
None.
Interview Justification
I would choose Binary Search because ordered boundary. I would not choose Linear scan ignores elimination because it does not match the property as directly.
Complexity
O(log n) time, O(1) space.
Reflection
The tempting shortcut is committing from the keyword instead of proving that Binary Search fits..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Linear scan ignores elimination
- 4.candidate refines by defending Binary Search
- 5.expert feedback: Strong if the candidate names the property before implementation..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptFoundation Problem 6: Range Sum Query. Answer many sum queries between left and right indices.
Interviewer review
Reader Worksheet
Signals
range, sum, many queries.
Properties
repeated range aggregation.
Candidate Patterns
Prefix Sum, brute force.
Verify Assumptions
Array is static.
Chosen Pattern
Prefix Sum.
Supporting Data Structures
Prefix array.
Interview Justification
I would choose Prefix Sum because repeated range aggregation. I would not choose Brute force repeats sums because it does not match the property as directly.
Complexity
O(n) build, O(1) query.
Reflection
The tempting shortcut is committing from the keyword instead of proving that Prefix Sum fits..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Brute force repeats sums
- 4.candidate refines by defending Prefix Sum
- 5.expert feedback: Strong if the candidate names the property before implementation..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptFoundation Problem 7: Contains Duplicate. Decide whether an array contains any duplicate.
Interviewer review
Reader Worksheet
Signals
duplicate, seen.
Properties
presence tracking.
Candidate Patterns
HashSet, sorting.
Verify Assumptions
Hashable values.
Chosen Pattern
HashSet.
Supporting Data Structures
HashSet.
Interview Justification
I would choose HashSet because presence tracking. I would not choose Sorting changes cost and may be unnecessary because it does not match the property as directly.
Complexity
O(n) time, O(n) space.
Reflection
The tempting shortcut is committing from the keyword instead of proving that HashSet fits..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Sorting changes cost and may be unnecessary
- 4.candidate refines by defending HashSet
- 5.expert feedback: Strong if the candidate names the property before implementation..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptFoundation Problem 8: Valid Palindrome. Determine whether a string is a palindrome ignoring non-alphanumeric characters.
Interviewer review
Reader Worksheet
Signals
palindrome, both ends.
Properties
symmetric comparison.
Candidate Patterns
Two Pointers, reverse string.
Verify Assumptions
Normalization rules are clear.
Chosen Pattern
Two Pointers.
Supporting Data Structures
None.
Interview Justification
I would choose Two Pointers because symmetric comparison. I would not choose Extra reversed copy unnecessary because it does not match the property as directly.
Complexity
O(n) time, O(1) space.
Reflection
The tempting shortcut is committing from the keyword instead of proving that Two Pointers fits..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Extra reversed copy unnecessary
- 4.candidate refines by defending Two Pointers
- 5.expert feedback: Strong if the candidate names the property before implementation..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptFoundation Problem 9: Maximum Depth of Binary Tree. Find the maximum depth of a binary tree.
Interviewer review
Reader Worksheet
Signals
tree, depth, maximum.
Properties
longest branch.
Candidate Patterns
DFS, BFS.
Verify Assumptions
Must visit relevant nodes.
Chosen Pattern
DFS.
Supporting Data Structures
Recursion or stack.
Interview Justification
I would choose DFS because longest branch. I would not choose BFS works but is less direct because it does not match the property as directly.
Complexity
O(n) time, O(h) space.
Reflection
The tempting shortcut is committing from the keyword instead of proving that DFS fits..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with BFS works but is less direct
- 4.candidate refines by defending DFS
- 5.expert feedback: Strong if the candidate names the property before implementation..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptFoundation Problem 10: Level Order Traversal. Return tree nodes level by level.
Interviewer review
Reader Worksheet
Signals
tree, level order.
Properties
layer-by-layer traversal.
Candidate Patterns
BFS, DFS with depth.
Verify Assumptions
Tree structure is available from root.
Chosen Pattern
BFS.
Supporting Data Structures
Queue.
Interview Justification
I would choose BFS because layer-by-layer traversal. I would not choose Plain DFS does not naturally preserve levels because it does not match the property as directly.
Complexity
O(n) time, O(w) space.
Reflection
The tempting shortcut is committing from the keyword instead of proving that BFS fits..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Plain DFS does not naturally preserve levels
- 4.candidate refines by defending BFS
- 5.expert feedback: Strong if the candidate names the property before implementation..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptFoundation Problem 11: Kth Largest Element. Find the kth largest value in an unsorted array.
Interviewer review
Reader Worksheet
Signals
kth, largest.
Properties
partial ordering.
Candidate Patterns
Heap, sorting, Quickselect.
Verify Assumptions
Only kth or top K matters.
Chosen Pattern
Heap or Quickselect.
Supporting Data Structures
Min-heap of size K.
Interview Justification
I would choose Heap or Quickselect because partial ordering. I would not choose Full sorting may do extra work because it does not match the property as directly.
Complexity
O(n log k) time, O(k) space.
Reflection
The tempting shortcut is committing from the keyword instead of proving that Heap or Quickselect fits..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Full sorting may do extra work
- 4.candidate refines by defending Heap or Quickselect
- 5.expert feedback: Strong if the candidate names the property before implementation..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptFoundation Problem 12: Find Minimum in Rotated Sorted Array. Find the minimum value in a rotated sorted array.
Interviewer review
Reader Worksheet
Signals
rotated, sorted, minimum.
Properties
partial order and boundary.
Candidate Patterns
Binary Search, scan.
Verify Assumptions
Rotation preserves sorted halves.
Chosen Pattern
Modified Binary Search.
Supporting Data Structures
None.
Interview Justification
I would choose Modified Binary Search because partial order and boundary. I would not choose Scan ignores ordering because it does not match the property as directly.
Complexity
O(log n) time, O(1) space.
Reflection
The tempting shortcut is committing from the keyword instead of proving that Modified Binary Search fits..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Scan ignores ordering
- 4.candidate refines by defending Modified Binary Search
- 5.expert feedback: Strong if the candidate names the property before implementation..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptFoundation Problem 13: Move Zeroes. Move all zeroes to the end while preserving non-zero order.
Interviewer review
Reader Worksheet
Signals
move, in-place, zeroes.
Properties
read/write positions.
Candidate Patterns
Two Pointers, extra array.
Verify Assumptions
Stable order required.
Chosen Pattern
Same-direction Two Pointers.
Supporting Data Structures
None.
Interview Justification
I would choose Same-direction Two Pointers because read/write positions. I would not choose Extra array not needed because it does not match the property as directly.
Complexity
O(n) time, O(1) space.
Reflection
The tempting shortcut is committing from the keyword instead of proving that Same-direction Two Pointers fits..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Extra array not needed
- 4.candidate refines by defending Same-direction Two Pointers
- 5.expert feedback: Strong if the candidate names the property before implementation..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptFoundation Problem 14: Group Anagrams. Group words that are anagrams.
Interviewer review
Reader Worksheet
Signals
group, anagram.
Properties
same signature belongs together.
Candidate Patterns
HashMap, sorting words.
Verify Assumptions
Stable signature can be built.
Chosen Pattern
HashMap grouping.
Supporting Data Structures
Map signature to list.
Interview Justification
I would choose HashMap grouping because same signature belongs together. I would not choose Two Pointers irrelevant because it does not match the property as directly.
Complexity
O(nk log k) or O(nk) depending signature.
Reflection
The tempting shortcut is committing from the keyword instead of proving that HashMap grouping fits..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Two Pointers irrelevant
- 4.candidate refines by defending HashMap grouping
- 5.expert feedback: Strong if the candidate names the property before implementation..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptFoundation Problem 15: Minimum Depth of Binary Tree. Find the minimum root-to-leaf depth.
Interviewer review
Reader Worksheet
Signals
tree, minimum, depth.
Properties
first leaf by level.
Candidate Patterns
BFS, DFS.
Verify Assumptions
First leaf reached by BFS is shortest.
Chosen Pattern
BFS.
Supporting Data Structures
Queue.
Interview Justification
I would choose BFS because first leaf by level. I would not choose DFS may explore deeper branches first because it does not match the property as directly.
Complexity
O(n) time, O(w) space.
Reflection
The tempting shortcut is committing from the keyword instead of proving that BFS fits..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with DFS may explore deeper branches first
- 4.candidate refines by defending BFS
- 5.expert feedback: Strong if the candidate names the property before implementation..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptFoundation Problem 16: First Bad Version. Find the first bad version using a monotonic API.
Interviewer review
Reader Worksheet
Signals
first, bad, version.
Properties
true/false boundary.
Candidate Patterns
Binary Search, linear scan.
Verify Assumptions
Bad remains bad after boundary.
Chosen Pattern
Binary Search.
Supporting Data Structures
None.
Interview Justification
I would choose Binary Search because true/false boundary. I would not choose Linear scan wastes monotonicity because it does not match the property as directly.
Complexity
O(log n) calls, O(1) space.
Reflection
The tempting shortcut is committing from the keyword instead of proving that Binary Search fits..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Linear scan wastes monotonicity
- 4.candidate refines by defending Binary Search
- 5.expert feedback: Strong if the candidate names the property before implementation..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptFoundation Problem 17: Top K Frequent Elements. Return the K most frequent numbers.
Interviewer review
Reader Worksheet
Signals
top K, frequent.
Properties
count then prioritize.
Candidate Patterns
HashMap + Heap, bucket sort, sorting.
Verify Assumptions
K is smaller than unique count or ranking matters.
Chosen Pattern
HashMap + Heap.
Supporting Data Structures
Map counts, heap ranks.
Interview Justification
I would choose HashMap + Heap because count then prioritize. I would not choose Heap alone cannot count because it does not match the property as directly.
Complexity
O(n log k) time, O(n) space.
Reflection
The tempting shortcut is committing from the keyword instead of proving that HashMap + Heap fits..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Heap alone cannot count
- 4.candidate refines by defending HashMap + Heap
- 5.expert feedback: Strong if the candidate names the property before implementation..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptFoundation Problem 18: Path Sum. Determine if a root-to-leaf path equals a target sum.
Interviewer review
Reader Worksheet
Signals
tree, path, sum.
Properties
branch state.
Candidate Patterns
DFS, BFS.
Verify Assumptions
Path must be root-to-leaf.
Chosen Pattern
DFS.
Supporting Data Structures
Recursion stack.
Interview Justification
I would choose DFS because branch state. I would not choose Prefix Sum over array does not apply directly because it does not match the property as directly.
Complexity
O(n) time, O(h) space.
Reflection
The tempting shortcut is committing from the keyword instead of proving that DFS fits..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Prefix Sum over array does not apply directly
- 4.candidate refines by defending DFS
- 5.expert feedback: Strong if the candidate names the property before implementation..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptFoundation Problem 19: Binary Search Target. Find a target in a sorted array.
Interviewer review
Reader Worksheet
Signals
sorted, target, search.
Properties
ordered elimination.
Candidate Patterns
Binary Search, scan.
Verify Assumptions
Array is sorted.
Chosen Pattern
Binary Search.
Supporting Data Structures
None.
Interview Justification
I would choose Binary Search because ordered elimination. I would not choose HashMap extra memory unnecessary because it does not match the property as directly.
Complexity
O(log n) time, O(1) space.
Reflection
The tempting shortcut is committing from the keyword instead of proving that Binary Search fits..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with HashMap extra memory unnecessary
- 4.candidate refines by defending Binary Search
- 5.expert feedback: Strong if the candidate names the property before implementation..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptFoundation Problem 20: Subarray Product Less Than K. Count contiguous subarrays with product less than K using positive numbers.
Interviewer review
Reader Worksheet
Signals
subarray, product, positive.
Properties
moving window with monotonic product.
Candidate Patterns
Sliding Window, brute force.
Verify Assumptions
All values are positive and K constraint is valid.
Chosen Pattern
Sliding Window.
Supporting Data Structures
None.
Interview Justification
I would choose Sliding Window because moving window with monotonic product. I would not choose Prefix Sum does not handle product cleanly because it does not match the property as directly.
Complexity
O(n) time, O(1) space.
Reflection
The tempting shortcut is committing from the keyword instead of proving that Sliding Window fits..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Prefix Sum does not handle product cleanly
- 4.candidate refines by defending Sliding Window
- 5.expert feedback: Strong if the candidate names the property before implementation..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptIntermediate Problem 21: Subarray Sum Equals K. Count subarrays whose sum equals K when negatives are allowed.
Interviewer review
Reader Worksheet
Signals
Subarray, Sum, Equals.
Properties
The core property points toward Prefix Sum + HashMap, not just the loudest keyword in the prompt..
Candidate Patterns
Prefix Sum + HashMap, Sliding Window, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
Prefix Sum + HashMap.
Supporting Data Structures
HashMap.
Interview Justification
I would choose Prefix Sum + HashMap because The core property points toward Prefix Sum + HashMap, not just the loudest keyword in the prompt.. I would not choose Sliding Window because it does not match the property as directly.
Complexity
Usually O(n) or O(n log n), depending on helper structure..
Reflection
What almost fools candidates is Sliding Window; the stronger signal is the property that supports Prefix Sum + HashMap..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Sliding Window
- 4.candidate refines by defending Prefix Sum + HashMap
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptIntermediate Problem 22: Container With Most Water. Find max water between two vertical lines.
Interviewer review
Reader Worksheet
Signals
Container, With, Most.
Properties
The core property points toward Two Pointers, not just the loudest keyword in the prompt..
Candidate Patterns
Two Pointers, DP, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
Two Pointers.
Supporting Data Structures
Depends on constraints.
Interview Justification
I would choose Two Pointers because The core property points toward Two Pointers, not just the loudest keyword in the prompt.. I would not choose DP because it does not match the property as directly.
Complexity
Usually O(n) with extra state, but verify constraints..
Reflection
What almost fools candidates is DP; the stronger signal is the property that supports Two Pointers..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with DP
- 4.candidate refines by defending Two Pointers
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptIntermediate Problem 23: Permutation in String. Check if one string contains a permutation of another.
Interviewer review
Reader Worksheet
Signals
Permutation, in, String.
Properties
The core property points toward Sliding Window + Frequency, not just the loudest keyword in the prompt..
Candidate Patterns
Sliding Window + Frequency, Backtracking, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
Sliding Window + Frequency.
Supporting Data Structures
HashMap or counters when needed.
Interview Justification
I would choose Sliding Window + Frequency because The core property points toward Sliding Window + Frequency, not just the loudest keyword in the prompt.. I would not choose Backtracking because it does not match the property as directly.
Complexity
Complexity depends on branching, heap size, or search range..
Reflection
What almost fools candidates is Backtracking; the stronger signal is the property that supports Sliding Window + Frequency..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Backtracking
- 4.candidate refines by defending Sliding Window + Frequency
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptIntermediate Problem 24: Find All Anagrams. Find all anagram start positions in a string.
Interviewer review
Reader Worksheet
Signals
Find, All, Anagrams.
Properties
The core property points toward Sliding Window + Frequency, not just the loudest keyword in the prompt..
Candidate Patterns
Sliding Window + Frequency, Sorting every substring, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
Sliding Window + Frequency.
Supporting Data Structures
HashMap or counters when needed.
Interview Justification
I would choose Sliding Window + Frequency because The core property points toward Sliding Window + Frequency, not just the loudest keyword in the prompt.. I would not choose Sorting every substring because it does not match the property as directly.
Complexity
Usually O(n) or O(n log n), depending on helper structure..
Reflection
What almost fools candidates is Sorting every substring; the stronger signal is the property that supports Sliding Window + Frequency..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Sorting every substring
- 4.candidate refines by defending Sliding Window + Frequency
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptIntermediate Problem 25: Search in Rotated Sorted Array. Find target in a rotated sorted array.
Interviewer review
Reader Worksheet
Signals
Search, in, Rotated.
Properties
The core property points toward Binary Search, not just the loudest keyword in the prompt..
Candidate Patterns
Binary Search, Linear scan, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
Binary Search.
Supporting Data Structures
Depends on constraints.
Interview Justification
I would choose Binary Search because The core property points toward Binary Search, not just the loudest keyword in the prompt.. I would not choose Linear scan because it does not match the property as directly.
Complexity
Usually O(n) with extra state, but verify constraints..
Reflection
What almost fools candidates is Linear scan; the stronger signal is the property that supports Binary Search..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Linear scan
- 4.candidate refines by defending Binary Search
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptIntermediate Problem 26: Validate BST. Check if a binary tree respects BST ordering.
Interviewer review
Reader Worksheet
Signals
Validate, BST.
Properties
The core property points toward DFS with bounds, not just the loudest keyword in the prompt..
Candidate Patterns
DFS with bounds, Local child-only checks, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
DFS with bounds.
Supporting Data Structures
Stack / recursion.
Interview Justification
I would choose DFS with bounds because The core property points toward DFS with bounds, not just the loudest keyword in the prompt.. I would not choose Local child-only checks because it does not match the property as directly.
Complexity
Complexity depends on branching, heap size, or search range..
Reflection
What almost fools candidates is Local child-only checks; the stronger signal is the property that supports DFS with bounds..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Local child-only checks
- 4.candidate refines by defending DFS with bounds
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptIntermediate Problem 27: Course Schedule. Decide if all courses can be completed.
Interviewer review
Reader Worksheet
Signals
Course, Schedule.
Properties
The core property points toward DFS/BFS graph cycle, not just the loudest keyword in the prompt..
Candidate Patterns
DFS/BFS graph cycle, Tree DFS without visited, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
DFS/BFS graph cycle.
Supporting Data Structures
Queue / visited set.
Interview Justification
I would choose DFS/BFS graph cycle because The core property points toward DFS/BFS graph cycle, not just the loudest keyword in the prompt.. I would not choose Tree DFS without visited because it does not match the property as directly.
Complexity
Usually O(n) or O(n log n), depending on helper structure..
Reflection
What almost fools candidates is Tree DFS without visited; the stronger signal is the property that supports DFS/BFS graph cycle..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Tree DFS without visited
- 4.candidate refines by defending DFS/BFS graph cycle
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptIntermediate Problem 28: Meeting Rooms II. Find minimum rooms required for intervals.
Interviewer review
Reader Worksheet
Signals
Meeting, Rooms, II.
Properties
The core property points toward Heap after sorting starts, not just the loudest keyword in the prompt..
Candidate Patterns
Heap after sorting starts, Nested scan, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
Heap after sorting starts.
Supporting Data Structures
Heap / Priority Queue.
Interview Justification
I would choose Heap after sorting starts because The core property points toward Heap after sorting starts, not just the loudest keyword in the prompt.. I would not choose Nested scan because it does not match the property as directly.
Complexity
Usually O(n) with extra state, but verify constraints..
Reflection
What almost fools candidates is Nested scan; the stronger signal is the property that supports Heap after sorting starts..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Nested scan
- 4.candidate refines by defending Heap after sorting starts
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptIntermediate Problem 29: Koko Eating Bananas. Find minimum eating speed within H hours.
Interviewer review
Reader Worksheet
Signals
Koko, Eating, Bananas.
Properties
The core property points toward Binary Search on Answer, not just the loudest keyword in the prompt..
Candidate Patterns
Binary Search on Answer, Sorting, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
Binary Search on Answer.
Supporting Data Structures
Depends on constraints.
Interview Justification
I would choose Binary Search on Answer because The core property points toward Binary Search on Answer, not just the loudest keyword in the prompt.. I would not choose Sorting because it does not match the property as directly.
Complexity
Complexity depends on branching, heap size, or search range..
Reflection
What almost fools candidates is Sorting; the stronger signal is the property that supports Binary Search on Answer..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Sorting
- 4.candidate refines by defending Binary Search on Answer
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptIntermediate Problem 30: Count Subarrays Divisible by K. Count subarrays whose sum is divisible by K.
Interviewer review
Reader Worksheet
Signals
Count, Subarrays, Divisible.
Properties
The core property points toward Prefix Sum + HashMap, not just the loudest keyword in the prompt..
Candidate Patterns
Prefix Sum + HashMap, Sliding Window, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
Prefix Sum + HashMap.
Supporting Data Structures
HashMap.
Interview Justification
I would choose Prefix Sum + HashMap because The core property points toward Prefix Sum + HashMap, not just the loudest keyword in the prompt.. I would not choose Sliding Window because it does not match the property as directly.
Complexity
Usually O(n) or O(n log n), depending on helper structure..
Reflection
What almost fools candidates is Sliding Window; the stronger signal is the property that supports Prefix Sum + HashMap..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Sliding Window
- 4.candidate refines by defending Prefix Sum + HashMap
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptIntermediate Problem 31: Clone Graph. Return a deep copy of an undirected graph.
Interviewer review
Reader Worksheet
Signals
Clone, Graph.
Properties
The core property points toward DFS/BFS + HashMap, not just the loudest keyword in the prompt..
Candidate Patterns
DFS/BFS + HashMap, Tree traversal only, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
DFS/BFS + HashMap.
Supporting Data Structures
HashMap.
Interview Justification
I would choose DFS/BFS + HashMap because The core property points toward DFS/BFS + HashMap, not just the loudest keyword in the prompt.. I would not choose Tree traversal only because it does not match the property as directly.
Complexity
Usually O(n) with extra state, but verify constraints..
Reflection
What almost fools candidates is Tree traversal only; the stronger signal is the property that supports DFS/BFS + HashMap..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Tree traversal only
- 4.candidate refines by defending DFS/BFS + HashMap
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptIntermediate Problem 32: Longest Repeating Character Replacement. Find longest substring after at most K replacements.
Interviewer review
Reader Worksheet
Signals
Longest, Repeating, Character.
Properties
The core property points toward Sliding Window + counts, not just the loudest keyword in the prompt..
Candidate Patterns
Sliding Window + counts, DP, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
Sliding Window + counts.
Supporting Data Structures
HashMap or counters when needed.
Interview Justification
I would choose Sliding Window + counts because The core property points toward Sliding Window + counts, not just the loudest keyword in the prompt.. I would not choose DP because it does not match the property as directly.
Complexity
Complexity depends on branching, heap size, or search range..
Reflection
What almost fools candidates is DP; the stronger signal is the property that supports Sliding Window + counts..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with DP
- 4.candidate refines by defending Sliding Window + counts
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptIntermediate Problem 33: Merge K Sorted Lists. Merge K sorted linked lists.
Interviewer review
Reader Worksheet
Signals
Merge, K, Sorted.
Properties
The core property points toward Heap / Priority Queue, not just the loudest keyword in the prompt..
Candidate Patterns
Heap / Priority Queue, Repeated full sorting, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
Heap / Priority Queue.
Supporting Data Structures
Heap / Priority Queue.
Interview Justification
I would choose Heap / Priority Queue because The core property points toward Heap / Priority Queue, not just the loudest keyword in the prompt.. I would not choose Repeated full sorting because it does not match the property as directly.
Complexity
Usually O(n) or O(n log n), depending on helper structure..
Reflection
What almost fools candidates is Repeated full sorting; the stronger signal is the property that supports Heap / Priority Queue..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Repeated full sorting
- 4.candidate refines by defending Heap / Priority Queue
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptIntermediate Problem 34: Find Peak Element. Find any peak index.
Interviewer review
Reader Worksheet
Signals
Find, Peak, Element.
Properties
The core property points toward Binary Search variant, not just the loudest keyword in the prompt..
Candidate Patterns
Binary Search variant, Heap, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
Binary Search variant.
Supporting Data Structures
Depends on constraints.
Interview Justification
I would choose Binary Search variant because The core property points toward Binary Search variant, not just the loudest keyword in the prompt.. I would not choose Heap because it does not match the property as directly.
Complexity
Usually O(n) with extra state, but verify constraints..
Reflection
What almost fools candidates is Heap; the stronger signal is the property that supports Binary Search variant..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Heap
- 4.candidate refines by defending Binary Search variant
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptIntermediate Problem 35: Lowest Common Ancestor. Find LCA in a binary tree.
Interviewer review
Reader Worksheet
Signals
Lowest, Common, Ancestor.
Properties
The core property points toward DFS, not just the loudest keyword in the prompt..
Candidate Patterns
DFS, BFS without parent map, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
DFS.
Supporting Data Structures
Stack / recursion.
Interview Justification
I would choose DFS because The core property points toward DFS, not just the loudest keyword in the prompt.. I would not choose BFS without parent map because it does not match the property as directly.
Complexity
Complexity depends on branching, heap size, or search range..
Reflection
What almost fools candidates is BFS without parent map; the stronger signal is the property that supports DFS..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with BFS without parent map
- 4.candidate refines by defending DFS
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptIntermediate Problem 36: Word Pattern. Check if pattern letters map bijectively to words.
Interviewer review
Reader Worksheet
Signals
Word, Pattern.
Properties
The core property points toward HashMap two-way mapping, not just the loudest keyword in the prompt..
Candidate Patterns
HashMap two-way mapping, One-way map, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
HashMap two-way mapping.
Supporting Data Structures
HashMap.
Interview Justification
I would choose HashMap two-way mapping because The core property points toward HashMap two-way mapping, not just the loudest keyword in the prompt.. I would not choose One-way map because it does not match the property as directly.
Complexity
Usually O(n) or O(n log n), depending on helper structure..
Reflection
What almost fools candidates is One-way map; the stronger signal is the property that supports HashMap two-way mapping..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with One-way map
- 4.candidate refines by defending HashMap two-way mapping
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptIntermediate Problem 37: Daily Temperatures. Days until warmer temperature.
Interviewer review
Reader Worksheet
Signals
Daily, Temperatures.
Properties
The core property points toward Monotonic stack, not just the loudest keyword in the prompt..
Candidate Patterns
Monotonic stack, Heap, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
Monotonic stack.
Supporting Data Structures
Depends on constraints.
Interview Justification
I would choose Monotonic stack because The core property points toward Monotonic stack, not just the loudest keyword in the prompt.. I would not choose Heap because it does not match the property as directly.
Complexity
Usually O(n) with extra state, but verify constraints..
Reflection
What almost fools candidates is Heap; the stronger signal is the property that supports Monotonic stack..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Heap
- 4.candidate refines by defending Monotonic stack
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptIntermediate Problem 38: Car Pooling. Check if trips exceed vehicle capacity.
Interviewer review
Reader Worksheet
Signals
Car, Pooling.
Properties
The core property points toward Difference Array / Sweep, not just the loudest keyword in the prompt..
Candidate Patterns
Difference Array / Sweep, Simulate every mile, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
Difference Array / Sweep.
Supporting Data Structures
Depends on constraints.
Interview Justification
I would choose Difference Array / Sweep because The core property points toward Difference Array / Sweep, not just the loudest keyword in the prompt.. I would not choose Simulate every mile because it does not match the property as directly.
Complexity
Complexity depends on branching, heap size, or search range..
Reflection
What almost fools candidates is Simulate every mile; the stronger signal is the property that supports Difference Array / Sweep..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Simulate every mile
- 4.candidate refines by defending Difference Array / Sweep
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptIntermediate Problem 39: K Closest Points. Return K points closest to origin.
Interviewer review
Reader Worksheet
Signals
K, Closest, Points.
Properties
The core property points toward Heap or Quickselect, not just the loudest keyword in the prompt..
Candidate Patterns
Heap or Quickselect, Full sort when K is small, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
Heap or Quickselect.
Supporting Data Structures
Heap / Priority Queue.
Interview Justification
I would choose Heap or Quickselect because The core property points toward Heap or Quickselect, not just the loudest keyword in the prompt.. I would not choose Full sort when K is small because it does not match the property as directly.
Complexity
Usually O(n) or O(n log n), depending on helper structure..
Reflection
What almost fools candidates is Full sort when K is small; the stronger signal is the property that supports Heap or Quickselect..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Full sort when K is small
- 4.candidate refines by defending Heap or Quickselect
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptIntermediate Problem 40: Minimum Size Subarray Sum. Find min length subarray with sum at least target and positive values.
Interviewer review
Reader Worksheet
Signals
Minimum, Size, Subarray.
Properties
The core property points toward Sliding Window, not just the loudest keyword in the prompt..
Candidate Patterns
Sliding Window, Prefix Sum + map, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
Sliding Window.
Supporting Data Structures
HashMap or counters when needed.
Interview Justification
I would choose Sliding Window because The core property points toward Sliding Window, not just the loudest keyword in the prompt.. I would not choose Prefix Sum + map because it does not match the property as directly.
Complexity
Usually O(n) with extra state, but verify constraints..
Reflection
What almost fools candidates is Prefix Sum + map; the stronger signal is the property that supports Sliding Window..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Prefix Sum + map
- 4.candidate refines by defending Sliding Window
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptIntermediate Problem 41: Binary Tree Right Side View. Return visible nodes from right side.
Interviewer review
Reader Worksheet
Signals
Binary, Tree, Right.
Properties
The core property points toward BFS by level or DFS depth, not just the loudest keyword in the prompt..
Candidate Patterns
BFS by level or DFS depth, Plain inorder, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
BFS by level or DFS depth.
Supporting Data Structures
Queue / visited set.
Interview Justification
I would choose BFS by level or DFS depth because The core property points toward BFS by level or DFS depth, not just the loudest keyword in the prompt.. I would not choose Plain inorder because it does not match the property as directly.
Complexity
Complexity depends on branching, heap size, or search range..
Reflection
What almost fools candidates is Plain inorder; the stronger signal is the property that supports BFS by level or DFS depth..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Plain inorder
- 4.candidate refines by defending BFS by level or DFS depth
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptIntermediate Problem 42: Find Median from Data Stream. Maintain median as numbers arrive.
Interviewer review
Reader Worksheet
Signals
Find, Median, from.
Properties
The core property points toward Two Heaps, not just the loudest keyword in the prompt..
Candidate Patterns
Two Heaps, Sort after every insert, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
Two Heaps.
Supporting Data Structures
Heap / Priority Queue.
Interview Justification
I would choose Two Heaps because The core property points toward Two Heaps, not just the loudest keyword in the prompt.. I would not choose Sort after every insert because it does not match the property as directly.
Complexity
Usually O(n) or O(n log n), depending on helper structure..
Reflection
What almost fools candidates is Sort after every insert; the stronger signal is the property that supports Two Heaps..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Sort after every insert
- 4.candidate refines by defending Two Heaps
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptIntermediate Problem 43: Maximum Subarray. Find maximum sum contiguous subarray.
Interviewer review
Reader Worksheet
Signals
Maximum, Subarray.
Properties
The core property points toward Kadane, not just the loudest keyword in the prompt..
Candidate Patterns
Kadane, Sliding Window with target, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
Kadane.
Supporting Data Structures
Depends on constraints.
Interview Justification
I would choose Kadane because The core property points toward Kadane, not just the loudest keyword in the prompt.. I would not choose Sliding Window with target because it does not match the property as directly.
Complexity
Usually O(n) with extra state, but verify constraints..
Reflection
What almost fools candidates is Sliding Window with target; the stronger signal is the property that supports Kadane..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Sliding Window with target
- 4.candidate refines by defending Kadane
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptIntermediate Problem 44: Sort Colors. Sort array of 0, 1, and 2 in-place.
Interviewer review
Reader Worksheet
Signals
Sort, Colors.
Properties
The core property points toward Three Pointers, not just the loudest keyword in the prompt..
Candidate Patterns
Three Pointers, Heap, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
Three Pointers.
Supporting Data Structures
Depends on constraints.
Interview Justification
I would choose Three Pointers because The core property points toward Three Pointers, not just the loudest keyword in the prompt.. I would not choose Heap because it does not match the property as directly.
Complexity
Complexity depends on branching, heap size, or search range..
Reflection
What almost fools candidates is Heap; the stronger signal is the property that supports Three Pointers..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Heap
- 4.candidate refines by defending Three Pointers
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptIntermediate Problem 45: Coin Change. Find minimum coins for an amount.
Interviewer review
Reader Worksheet
Signals
Coin, Change.
Properties
The core property points toward Dynamic Programming, not just the loudest keyword in the prompt..
Candidate Patterns
Dynamic Programming, Greedy, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
Dynamic Programming.
Supporting Data Structures
Depends on constraints.
Interview Justification
I would choose Dynamic Programming because The core property points toward Dynamic Programming, not just the loudest keyword in the prompt.. I would not choose Greedy because it does not match the property as directly.
Complexity
Usually O(n) or O(n log n), depending on helper structure..
Reflection
What almost fools candidates is Greedy; the stronger signal is the property that supports Dynamic Programming..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Greedy
- 4.candidate refines by defending Dynamic Programming
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptHybrid Problem 46: Sliding Window Maximum. Return max for every window of size K.
Interviewer review
Reader Worksheet
Signals
Sliding, Window, Maximum.
Properties
The core property points toward Monotonic Deque, not just the loudest keyword in the prompt..
Candidate Patterns
Monotonic Deque, Heap without lazy deletion, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
Monotonic Deque.
Supporting Data Structures
Depends on constraints.
Interview Justification
I would choose Monotonic Deque because The core property points toward Monotonic Deque, not just the loudest keyword in the prompt.. I would not choose Heap without lazy deletion because it does not match the property as directly.
Complexity
Usually O(n) with extra state, but verify constraints..
Reflection
What almost fools candidates is Heap without lazy deletion; the stronger signal is the property that supports Monotonic Deque..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Heap without lazy deletion
- 4.candidate refines by defending Monotonic Deque
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptHybrid Problem 47: Maximum Size Subarray Sum Equals K. Find longest subarray summing to K.
Interviewer review
Reader Worksheet
Signals
Maximum, Size, Subarray.
Properties
The core property points toward Prefix Sum + HashMap, not just the loudest keyword in the prompt..
Candidate Patterns
Prefix Sum + HashMap, Sliding Window with negatives, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
Prefix Sum + HashMap.
Supporting Data Structures
HashMap.
Interview Justification
I would choose Prefix Sum + HashMap because The core property points toward Prefix Sum + HashMap, not just the loudest keyword in the prompt.. I would not choose Sliding Window with negatives because it does not match the property as directly.
Complexity
Complexity depends on branching, heap size, or search range..
Reflection
What almost fools candidates is Sliding Window with negatives; the stronger signal is the property that supports Prefix Sum + HashMap..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Sliding Window with negatives
- 4.candidate refines by defending Prefix Sum + HashMap
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptHybrid Problem 48: Network Delay Time. Find time for signal to reach all nodes.
Interviewer review
Reader Worksheet
Signals
Network, Delay, Time.
Properties
The core property points toward Dijkstra + Heap, not just the loudest keyword in the prompt..
Candidate Patterns
Dijkstra + Heap, Plain BFS, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
Dijkstra + Heap.
Supporting Data Structures
Heap / Priority Queue.
Interview Justification
I would choose Dijkstra + Heap because The core property points toward Dijkstra + Heap, not just the loudest keyword in the prompt.. I would not choose Plain BFS because it does not match the property as directly.
Complexity
Usually O(n) or O(n log n), depending on helper structure..
Reflection
What almost fools candidates is Plain BFS; the stronger signal is the property that supports Dijkstra + Heap..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Plain BFS
- 4.candidate refines by defending Dijkstra + Heap
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptHybrid Problem 49: Accounts Merge. Merge accounts by shared emails.
Interviewer review
Reader Worksheet
Signals
Accounts, Merge.
Properties
The core property points toward DFS/Union Find + HashMap, not just the loudest keyword in the prompt..
Candidate Patterns
DFS/Union Find + HashMap, Sorting only, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
DFS/Union Find + HashMap.
Supporting Data Structures
HashMap.
Interview Justification
I would choose DFS/Union Find + HashMap because The core property points toward DFS/Union Find + HashMap, not just the loudest keyword in the prompt.. I would not choose Sorting only because it does not match the property as directly.
Complexity
Usually O(n) with extra state, but verify constraints..
Reflection
What almost fools candidates is Sorting only; the stronger signal is the property that supports DFS/Union Find + HashMap..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Sorting only
- 4.candidate refines by defending DFS/Union Find + HashMap
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptHybrid Problem 50: Word Ladder. Shortest transformation sequence length.
Interviewer review
Reader Worksheet
Signals
Word, Ladder.
Properties
The core property points toward BFS + pattern map, not just the loudest keyword in the prompt..
Candidate Patterns
BFS + pattern map, DFS, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
BFS + pattern map.
Supporting Data Structures
Queue / visited set.
Interview Justification
I would choose BFS + pattern map because The core property points toward BFS + pattern map, not just the loudest keyword in the prompt.. I would not choose DFS because it does not match the property as directly.
Complexity
Complexity depends on branching, heap size, or search range..
Reflection
What almost fools candidates is DFS; the stronger signal is the property that supports BFS + pattern map..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with DFS
- 4.candidate refines by defending BFS + pattern map
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptHybrid Problem 51: Task Scheduler. Schedule tasks with cooldown.
Interviewer review
Reader Worksheet
Signals
Task, Scheduler.
Properties
The core property points toward Heap + Queue or Greedy, not just the loudest keyword in the prompt..
Candidate Patterns
Heap + Queue or Greedy, Simple sorting, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
Heap + Queue or Greedy.
Supporting Data Structures
Heap / Priority Queue.
Interview Justification
I would choose Heap + Queue or Greedy because The core property points toward Heap + Queue or Greedy, not just the loudest keyword in the prompt.. I would not choose Simple sorting because it does not match the property as directly.
Complexity
Usually O(n) or O(n log n), depending on helper structure..
Reflection
What almost fools candidates is Simple sorting; the stronger signal is the property that supports Heap + Queue or Greedy..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Simple sorting
- 4.candidate refines by defending Heap + Queue or Greedy
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptHybrid Problem 52: Serialize and Deserialize Binary Tree. Encode and decode a binary tree.
Interviewer review
Reader Worksheet
Signals
Serialize, and, Deserialize.
Properties
The core property points toward DFS/BFS + markers, not just the loudest keyword in the prompt..
Candidate Patterns
DFS/BFS + markers, HashMap, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
DFS/BFS + markers.
Supporting Data Structures
Queue / visited set.
Interview Justification
I would choose DFS/BFS + markers because The core property points toward DFS/BFS + markers, not just the loudest keyword in the prompt.. I would not choose HashMap because it does not match the property as directly.
Complexity
Usually O(n) with extra state, but verify constraints..
Reflection
What almost fools candidates is HashMap; the stronger signal is the property that supports DFS/BFS + markers..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with HashMap
- 4.candidate refines by defending DFS/BFS + markers
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptHybrid Problem 53: Split Array Largest Sum. Minimize largest subarray sum after splitting.
Interviewer review
Reader Worksheet
Signals
Split, Array, Largest.
Properties
The core property points toward Binary Search + Greedy, not just the loudest keyword in the prompt..
Candidate Patterns
Binary Search + Greedy, DP only, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
Binary Search + Greedy.
Supporting Data Structures
Depends on constraints.
Interview Justification
I would choose Binary Search + Greedy because The core property points toward Binary Search + Greedy, not just the loudest keyword in the prompt.. I would not choose DP only because it does not match the property as directly.
Complexity
Complexity depends on branching, heap size, or search range..
Reflection
What almost fools candidates is DP only; the stronger signal is the property that supports Binary Search + Greedy..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with DP only
- 4.candidate refines by defending Binary Search + Greedy
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptHybrid Problem 54: Best Time to Buy/Sell Stock with Cooldown. Max profit with cooldown after sell.
Interviewer review
Reader Worksheet
Signals
Best, Time, to.
Properties
The core property points toward Dynamic Programming, not just the loudest keyword in the prompt..
Candidate Patterns
Dynamic Programming, Two Pointers, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
Dynamic Programming.
Supporting Data Structures
Depends on constraints.
Interview Justification
I would choose Dynamic Programming because The core property points toward Dynamic Programming, not just the loudest keyword in the prompt.. I would not choose Two Pointers because it does not match the property as directly.
Complexity
Usually O(n) or O(n log n), depending on helper structure..
Reflection
What almost fools candidates is Two Pointers; the stronger signal is the property that supports Dynamic Programming..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Two Pointers
- 4.candidate refines by defending Dynamic Programming
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptHybrid Problem 55: Combination Sum. Find combinations that sum to target.
Interviewer review
Reader Worksheet
Signals
Combination, Sum.
Properties
The core property points toward Backtracking, not just the loudest keyword in the prompt..
Candidate Patterns
Backtracking, DP count only, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
Backtracking.
Supporting Data Structures
Depends on constraints.
Interview Justification
I would choose Backtracking because The core property points toward Backtracking, not just the loudest keyword in the prompt.. I would not choose DP count only because it does not match the property as directly.
Complexity
Usually O(n) with extra state, but verify constraints..
Reflection
What almost fools candidates is DP count only; the stronger signal is the property that supports Backtracking..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with DP count only
- 4.candidate refines by defending Backtracking
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptHybrid Problem 56: Palindrome Partitioning. Partition string into palindromic substrings.
Interviewer review
Reader Worksheet
Signals
Palindrome, Partitioning.
Properties
The core property points toward Backtracking + DP precheck, not just the loudest keyword in the prompt..
Candidate Patterns
Backtracking + DP precheck, Sliding Window, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
Backtracking + DP precheck.
Supporting Data Structures
Depends on constraints.
Interview Justification
I would choose Backtracking + DP precheck because The core property points toward Backtracking + DP precheck, not just the loudest keyword in the prompt.. I would not choose Sliding Window because it does not match the property as directly.
Complexity
Complexity depends on branching, heap size, or search range..
Reflection
What almost fools candidates is Sliding Window; the stronger signal is the property that supports Backtracking + DP precheck..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Sliding Window
- 4.candidate refines by defending Backtracking + DP precheck
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptHybrid Problem 57: Alien Dictionary. Infer character order from sorted words.
Interviewer review
Reader Worksheet
Signals
Alien, Dictionary.
Properties
The core property points toward Graph BFS/DFS, not just the loudest keyword in the prompt..
Candidate Patterns
Graph BFS/DFS, Sorting again, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
Graph BFS/DFS.
Supporting Data Structures
Queue / visited set.
Interview Justification
I would choose Graph BFS/DFS because The core property points toward Graph BFS/DFS, not just the loudest keyword in the prompt.. I would not choose Sorting again because it does not match the property as directly.
Complexity
Usually O(n) or O(n log n), depending on helper structure..
Reflection
What almost fools candidates is Sorting again; the stronger signal is the property that supports Graph BFS/DFS..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Sorting again
- 4.candidate refines by defending Graph BFS/DFS
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptHybrid Problem 58: Find Duplicate Subtrees. Detect duplicate subtrees.
Interviewer review
Reader Worksheet
Signals
Find, Duplicate, Subtrees.
Properties
The core property points toward DFS + HashMap serialization, not just the loudest keyword in the prompt..
Candidate Patterns
DFS + HashMap serialization, BFS levels, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
DFS + HashMap serialization.
Supporting Data Structures
HashMap.
Interview Justification
I would choose DFS + HashMap serialization because The core property points toward DFS + HashMap serialization, not just the loudest keyword in the prompt.. I would not choose BFS levels because it does not match the property as directly.
Complexity
Usually O(n) with extra state, but verify constraints..
Reflection
What almost fools candidates is BFS levels; the stronger signal is the property that supports DFS + HashMap serialization..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with BFS levels
- 4.candidate refines by defending DFS + HashMap serialization
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptHybrid Problem 59: LRU Cache. Implement get and put with recency.
Interviewer review
Reader Worksheet
Signals
LRU, Cache.
Properties
The core property points toward HashMap + Doubly Linked List, not just the loudest keyword in the prompt..
Candidate Patterns
HashMap + Doubly Linked List, Heap, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
HashMap + Doubly Linked List.
Supporting Data Structures
HashMap.
Interview Justification
I would choose HashMap + Doubly Linked List because The core property points toward HashMap + Doubly Linked List, not just the loudest keyword in the prompt.. I would not choose Heap because it does not match the property as directly.
Complexity
Complexity depends on branching, heap size, or search range..
Reflection
What almost fools candidates is Heap; the stronger signal is the property that supports HashMap + Doubly Linked List..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Heap
- 4.candidate refines by defending HashMap + Doubly Linked List
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptHybrid Problem 60: Minimum Window Substring. Find smallest window containing all chars.
Interviewer review
Reader Worksheet
Signals
Minimum, Window, Substring.
Properties
The core property points toward Sliding Window + HashMap, not just the loudest keyword in the prompt..
Candidate Patterns
Sliding Window + HashMap, Prefix Sum, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
Sliding Window + HashMap.
Supporting Data Structures
HashMap.
Interview Justification
I would choose Sliding Window + HashMap because The core property points toward Sliding Window + HashMap, not just the loudest keyword in the prompt.. I would not choose Prefix Sum because it does not match the property as directly.
Complexity
Usually O(n) or O(n log n), depending on helper structure..
Reflection
What almost fools candidates is Prefix Sum; the stronger signal is the property that supports Sliding Window + HashMap..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Prefix Sum
- 4.candidate refines by defending Sliding Window + HashMap
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptHybrid Problem 61: Longest Consecutive Sequence. Find longest consecutive values.
Interviewer review
Reader Worksheet
Signals
Longest, Consecutive, Sequence.
Properties
The core property points toward HashSet, not just the loudest keyword in the prompt..
Candidate Patterns
HashSet, Sliding Window, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
HashSet.
Supporting Data Structures
Depends on constraints.
Interview Justification
I would choose HashSet because The core property points toward HashSet, not just the loudest keyword in the prompt.. I would not choose Sliding Window because it does not match the property as directly.
Complexity
Usually O(n) with extra state, but verify constraints..
Reflection
What almost fools candidates is Sliding Window; the stronger signal is the property that supports HashSet..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Sliding Window
- 4.candidate refines by defending HashSet
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptHybrid Problem 62: Trapping Rain Water. Compute trapped rainwater.
Interviewer review
Reader Worksheet
Signals
Trapping, Rain, Water.
Properties
The core property points toward Two Pointers / Prefix Max, not just the loudest keyword in the prompt..
Candidate Patterns
Two Pointers / Prefix Max, Heap for 1D, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
Two Pointers / Prefix Max.
Supporting Data Structures
Depends on constraints.
Interview Justification
I would choose Two Pointers / Prefix Max because The core property points toward Two Pointers / Prefix Max, not just the loudest keyword in the prompt.. I would not choose Heap for 1D because it does not match the property as directly.
Complexity
Complexity depends on branching, heap size, or search range..
Reflection
What almost fools candidates is Heap for 1D; the stronger signal is the property that supports Two Pointers / Prefix Max..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Heap for 1D
- 4.candidate refines by defending Two Pointers / Prefix Max
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptHybrid Problem 63: Unique Paths. Count grid paths.
Interviewer review
Reader Worksheet
Signals
Unique, Paths.
Properties
The core property points toward Dynamic Programming, not just the loudest keyword in the prompt..
Candidate Patterns
Dynamic Programming, DFS brute force, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
Dynamic Programming.
Supporting Data Structures
Depends on constraints.
Interview Justification
I would choose Dynamic Programming because The core property points toward Dynamic Programming, not just the loudest keyword in the prompt.. I would not choose DFS brute force because it does not match the property as directly.
Complexity
Usually O(n) or O(n log n), depending on helper structure..
Reflection
What almost fools candidates is DFS brute force; the stronger signal is the property that supports Dynamic Programming..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with DFS brute force
- 4.candidate refines by defending Dynamic Programming
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptHybrid Problem 64: N Queens. Place N queens safely.
Interviewer review
Reader Worksheet
Signals
N, Queens.
Properties
The core property points toward Backtracking + Sets, not just the loudest keyword in the prompt..
Candidate Patterns
Backtracking + Sets, Greedy, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
Backtracking + Sets.
Supporting Data Structures
Depends on constraints.
Interview Justification
I would choose Backtracking + Sets because The core property points toward Backtracking + Sets, not just the loudest keyword in the prompt.. I would not choose Greedy because it does not match the property as directly.
Complexity
Usually O(n) with extra state, but verify constraints..
Reflection
What almost fools candidates is Greedy; the stronger signal is the property that supports Backtracking + Sets..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Greedy
- 4.candidate refines by defending Backtracking + Sets
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptHybrid Problem 65: Corporate Flight Bookings. Apply bookings over ranges.
Interviewer review
Reader Worksheet
Signals
Corporate, Flight, Bookings.
Properties
The core property points toward Difference Array, not just the loudest keyword in the prompt..
Candidate Patterns
Difference Array, Nested updates, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
Difference Array.
Supporting Data Structures
Depends on constraints.
Interview Justification
I would choose Difference Array because The core property points toward Difference Array, not just the loudest keyword in the prompt.. I would not choose Nested updates because it does not match the property as directly.
Complexity
Complexity depends on branching, heap size, or search range..
Reflection
What almost fools candidates is Nested updates; the stronger signal is the property that supports Difference Array..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Nested updates
- 4.candidate refines by defending Difference Array
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptTraps Problem 66: Subarray Sum with Negatives. Find if any subarray equals K with negative numbers.
Interviewer review
Reader Worksheet
Signals
Subarray, Sum, with.
Properties
The core property points toward Prefix Sum + HashMap, not just the loudest keyword in the prompt..
Candidate Patterns
Prefix Sum + HashMap, Sliding Window, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
Prefix Sum + HashMap.
Supporting Data Structures
HashMap.
Interview Justification
I would choose Prefix Sum + HashMap because The core property points toward Prefix Sum + HashMap, not just the loudest keyword in the prompt.. I would not choose Sliding Window because it does not match the property as directly.
Complexity
Usually O(n) or O(n log n), depending on helper structure..
Reflection
What almost fools candidates is Sliding Window; the stronger signal is the property that supports Prefix Sum + HashMap..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Sliding Window
- 4.candidate refines by defending Prefix Sum + HashMap
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptTraps Problem 67: Sorted Pair Closest to Target. Find pair closest to target in sorted array.
Interviewer review
Reader Worksheet
Signals
Sorted, Pair, Closest.
Properties
The core property points toward Two Pointers, not just the loudest keyword in the prompt..
Candidate Patterns
Two Pointers, Binary Search only, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
Two Pointers.
Supporting Data Structures
Depends on constraints.
Interview Justification
I would choose Two Pointers because The core property points toward Two Pointers, not just the loudest keyword in the prompt.. I would not choose Binary Search only because it does not match the property as directly.
Complexity
Usually O(n) with extra state, but verify constraints..
Reflection
What almost fools candidates is Binary Search only; the stronger signal is the property that supports Two Pointers..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Binary Search only
- 4.candidate refines by defending Two Pointers
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptTraps Problem 68: Tree Level Averages. Return average value at each tree level.
Interviewer review
Reader Worksheet
Signals
Tree, Level, Averages.
Properties
The core property points toward BFS, not just the loudest keyword in the prompt..
Candidate Patterns
BFS, DFS without level state, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
BFS.
Supporting Data Structures
Queue / visited set.
Interview Justification
I would choose BFS because The core property points toward BFS, not just the loudest keyword in the prompt.. I would not choose DFS without level state because it does not match the property as directly.
Complexity
Complexity depends on branching, heap size, or search range..
Reflection
What almost fools candidates is DFS without level state; the stronger signal is the property that supports BFS..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with DFS without level state
- 4.candidate refines by defending BFS
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptTraps Problem 69: Permutation Generation. Generate all permutations.
Interviewer review
Reader Worksheet
Signals
Permutation, Generation.
Properties
The core property points toward Backtracking, not just the loudest keyword in the prompt..
Candidate Patterns
Backtracking, Sorting, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
Backtracking.
Supporting Data Structures
Depends on constraints.
Interview Justification
I would choose Backtracking because The core property points toward Backtracking, not just the loudest keyword in the prompt.. I would not choose Sorting because it does not match the property as directly.
Complexity
Usually O(n) or O(n log n), depending on helper structure..
Reflection
What almost fools candidates is Sorting; the stronger signal is the property that supports Backtracking..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Sorting
- 4.candidate refines by defending Backtracking
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptTraps Problem 70: Maximum Product Subarray. Find maximum product subarray.
Interviewer review
Reader Worksheet
Signals
Maximum, Product, Subarray.
Properties
The core property points toward DP tracking max/min, not just the loudest keyword in the prompt..
Candidate Patterns
DP tracking max/min, Sliding Window, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
DP tracking max/min.
Supporting Data Structures
Depends on constraints.
Interview Justification
I would choose DP tracking max/min because The core property points toward DP tracking max/min, not just the loudest keyword in the prompt.. I would not choose Sliding Window because it does not match the property as directly.
Complexity
Usually O(n) with extra state, but verify constraints..
Reflection
What almost fools candidates is Sliding Window; the stronger signal is the property that supports DP tracking max/min..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Sliding Window
- 4.candidate refines by defending DP tracking max/min
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptTraps Problem 71: Rotten Oranges. Minutes until all oranges rot.
Interviewer review
Reader Worksheet
Signals
Rotten, Oranges.
Properties
The core property points toward BFS multi-source, not just the loudest keyword in the prompt..
Candidate Patterns
BFS multi-source, DFS, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
BFS multi-source.
Supporting Data Structures
Queue / visited set.
Interview Justification
I would choose BFS multi-source because The core property points toward BFS multi-source, not just the loudest keyword in the prompt.. I would not choose DFS because it does not match the property as directly.
Complexity
Complexity depends on branching, heap size, or search range..
Reflection
What almost fools candidates is DFS; the stronger signal is the property that supports BFS multi-source..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with DFS
- 4.candidate refines by defending BFS multi-source
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptTraps Problem 72: First Missing Positive. Find smallest missing positive integer.
Interviewer review
Reader Worksheet
Signals
First, Missing, Positive.
Properties
The core property points toward Index placement, not just the loudest keyword in the prompt..
Candidate Patterns
Index placement, HashMap as first choice, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
Index placement.
Supporting Data Structures
Depends on constraints.
Interview Justification
I would choose Index placement because The core property points toward Index placement, not just the loudest keyword in the prompt.. I would not choose HashMap as first choice because it does not match the property as directly.
Complexity
Usually O(n) or O(n log n), depending on helper structure..
Reflection
What almost fools candidates is HashMap as first choice; the stronger signal is the property that supports Index placement..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with HashMap as first choice
- 4.candidate refines by defending Index placement
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptTraps Problem 73: Median of Two Sorted Arrays. Find median across two sorted arrays.
Interviewer review
Reader Worksheet
Signals
Median, of, Two.
Properties
The core property points toward Binary Search partition, not just the loudest keyword in the prompt..
Candidate Patterns
Binary Search partition, Merge everything, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
Binary Search partition.
Supporting Data Structures
Depends on constraints.
Interview Justification
I would choose Binary Search partition because The core property points toward Binary Search partition, not just the loudest keyword in the prompt.. I would not choose Merge everything because it does not match the property as directly.
Complexity
Usually O(n) with extra state, but verify constraints..
Reflection
What almost fools candidates is Merge everything; the stronger signal is the property that supports Binary Search partition..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Merge everything
- 4.candidate refines by defending Binary Search partition
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptTraps Problem 74: All Paths From Source to Target. Return all DAG paths.
Interviewer review
Reader Worksheet
Signals
All, Paths, From.
Properties
The core property points toward DFS Backtracking, not just the loudest keyword in the prompt..
Candidate Patterns
DFS Backtracking, BFS shortest path, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
DFS Backtracking.
Supporting Data Structures
Stack / recursion.
Interview Justification
I would choose DFS Backtracking because The core property points toward DFS Backtracking, not just the loudest keyword in the prompt.. I would not choose BFS shortest path because it does not match the property as directly.
Complexity
Complexity depends on branching, heap size, or search range..
Reflection
What almost fools candidates is BFS shortest path; the stronger signal is the property that supports DFS Backtracking..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with BFS shortest path
- 4.candidate refines by defending DFS Backtracking
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptTraps Problem 75: Top K Frequent Words. Return top K words by frequency and lexicographic order.
Interviewer review
Reader Worksheet
Signals
Top, K, Frequent.
Properties
The core property points toward HashMap + Heap/Sort, not just the loudest keyword in the prompt..
Candidate Patterns
HashMap + Heap/Sort, Heap without tie rules, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
HashMap + Heap/Sort.
Supporting Data Structures
HashMap.
Interview Justification
I would choose HashMap + Heap/Sort because The core property points toward HashMap + Heap/Sort, not just the loudest keyword in the prompt.. I would not choose Heap without tie rules because it does not match the property as directly.
Complexity
Usually O(n) or O(n log n), depending on helper structure..
Reflection
What almost fools candidates is Heap without tie rules; the stronger signal is the property that supports HashMap + Heap/Sort..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Heap without tie rules
- 4.candidate refines by defending HashMap + Heap/Sort
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptTraps Problem 76: Maximum Width of Binary Tree. Find max width using position indices.
Interviewer review
Reader Worksheet
Signals
Maximum, Width, of.
Properties
The core property points toward BFS with indices, not just the loudest keyword in the prompt..
Candidate Patterns
BFS with indices, Plain DFS depth, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
BFS with indices.
Supporting Data Structures
Queue / visited set.
Interview Justification
I would choose BFS with indices because The core property points toward BFS with indices, not just the loudest keyword in the prompt.. I would not choose Plain DFS depth because it does not match the property as directly.
Complexity
Usually O(n) with extra state, but verify constraints..
Reflection
What almost fools candidates is Plain DFS depth; the stronger signal is the property that supports BFS with indices..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Plain DFS depth
- 4.candidate refines by defending BFS with indices
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptTraps Problem 77: Edit Distance. Minimum operations to convert word A to B.
Interviewer review
Reader Worksheet
Signals
Edit, Distance.
Properties
The core property points toward Dynamic Programming, not just the loudest keyword in the prompt..
Candidate Patterns
Dynamic Programming, Two Pointers, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
Dynamic Programming.
Supporting Data Structures
Depends on constraints.
Interview Justification
I would choose Dynamic Programming because The core property points toward Dynamic Programming, not just the loudest keyword in the prompt.. I would not choose Two Pointers because it does not match the property as directly.
Complexity
Complexity depends on branching, heap size, or search range..
Reflection
What almost fools candidates is Two Pointers; the stronger signal is the property that supports Dynamic Programming..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Two Pointers
- 4.candidate refines by defending Dynamic Programming
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptTraps Problem 78: Longest Palindromic Substring. Find longest palindromic substring.
Interviewer review
Reader Worksheet
Signals
Longest, Palindromic, Substring.
Properties
The core property points toward Expand around center / DP, not just the loudest keyword in the prompt..
Candidate Patterns
Expand around center / DP, Sliding Window, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
Expand around center / DP.
Supporting Data Structures
Depends on constraints.
Interview Justification
I would choose Expand around center / DP because The core property points toward Expand around center / DP, not just the loudest keyword in the prompt.. I would not choose Sliding Window because it does not match the property as directly.
Complexity
Usually O(n) or O(n log n), depending on helper structure..
Reflection
What almost fools candidates is Sliding Window; the stronger signal is the property that supports Expand around center / DP..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Sliding Window
- 4.candidate refines by defending Expand around center / DP
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptTraps Problem 79: Find Kth Smallest in BST. Find kth smallest value in BST.
Interviewer review
Reader Worksheet
Signals
Find, Kth, Smallest.
Properties
The core property points toward Inorder DFS, not just the loudest keyword in the prompt..
Candidate Patterns
Inorder DFS, Heap, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
Inorder DFS.
Supporting Data Structures
Stack / recursion.
Interview Justification
I would choose Inorder DFS because The core property points toward Inorder DFS, not just the loudest keyword in the prompt.. I would not choose Heap because it does not match the property as directly.
Complexity
Usually O(n) with extra state, but verify constraints..
Reflection
What almost fools candidates is Heap; the stronger signal is the property that supports Inorder DFS..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Heap
- 4.candidate refines by defending Inorder DFS
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptTraps Problem 80: Jump Game. Determine if end is reachable.
Interviewer review
Reader Worksheet
Signals
Jump, Game.
Properties
The core property points toward Greedy / DP, not just the loudest keyword in the prompt..
Candidate Patterns
Greedy / DP, BFS over all jumps, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
Greedy / DP.
Supporting Data Structures
Depends on constraints.
Interview Justification
I would choose Greedy / DP because The core property points toward Greedy / DP, not just the loudest keyword in the prompt.. I would not choose BFS over all jumps because it does not match the property as directly.
Complexity
Complexity depends on branching, heap size, or search range..
Reflection
What almost fools candidates is BFS over all jumps; the stronger signal is the property that supports Greedy / DP..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with BFS over all jumps
- 4.candidate refines by defending Greedy / DP
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptTraps Problem 81: Meeting Rooms I. Can attend all meetings?
Interviewer review
Reader Worksheet
Signals
Meeting, Rooms, I.
Properties
The core property points toward Sorting intervals, not just the loudest keyword in the prompt..
Candidate Patterns
Sorting intervals, Heap, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
Sorting intervals.
Supporting Data Structures
Depends on constraints.
Interview Justification
I would choose Sorting intervals because The core property points toward Sorting intervals, not just the loudest keyword in the prompt.. I would not choose Heap because it does not match the property as directly.
Complexity
Usually O(n) or O(n log n), depending on helper structure..
Reflection
What almost fools candidates is Heap; the stronger signal is the property that supports Sorting intervals..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Heap
- 4.candidate refines by defending Sorting intervals
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptTraps Problem 82: Subsets. Generate all subsets.
Interviewer review
Reader Worksheet
Signals
Subsets.
Properties
The core property points toward Backtracking, not just the loudest keyword in the prompt..
Candidate Patterns
Backtracking, Bit count HashMap, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
Backtracking.
Supporting Data Structures
Depends on constraints.
Interview Justification
I would choose Backtracking because The core property points toward Backtracking, not just the loudest keyword in the prompt.. I would not choose Bit count HashMap because it does not match the property as directly.
Complexity
Usually O(n) with extra state, but verify constraints..
Reflection
What almost fools candidates is Bit count HashMap; the stronger signal is the property that supports Backtracking..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Bit count HashMap
- 4.candidate refines by defending Backtracking
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptTraps Problem 83: Shortest Path in Binary Matrix. Shortest 8-direction path.
Interviewer review
Reader Worksheet
Signals
Shortest, Path, in.
Properties
The core property points toward BFS, not just the loudest keyword in the prompt..
Candidate Patterns
BFS, DP, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
BFS.
Supporting Data Structures
Queue / visited set.
Interview Justification
I would choose BFS because The core property points toward BFS, not just the loudest keyword in the prompt.. I would not choose DP because it does not match the property as directly.
Complexity
Complexity depends on branching, heap size, or search range..
Reflection
What almost fools candidates is DP; the stronger signal is the property that supports BFS..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with DP
- 4.candidate refines by defending BFS
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptTraps Problem 84: Find All Numbers Disappeared. Find missing values from 1..n.
Interviewer review
Reader Worksheet
Signals
Find, All, Numbers.
Properties
The core property points toward Index marking, not just the loudest keyword in the prompt..
Candidate Patterns
Index marking, HashMap, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
Index marking.
Supporting Data Structures
Depends on constraints.
Interview Justification
I would choose Index marking because The core property points toward Index marking, not just the loudest keyword in the prompt.. I would not choose HashMap because it does not match the property as directly.
Complexity
Usually O(n) or O(n log n), depending on helper structure..
Reflection
What almost fools candidates is HashMap; the stronger signal is the property that supports Index marking..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with HashMap
- 4.candidate refines by defending Index marking
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptTraps Problem 85: Longest Increasing Subsequence. Find LIS length.
Interviewer review
Reader Worksheet
Signals
Longest, Increasing, Subsequence.
Properties
The core property points toward DP / Binary Search tails, not just the loudest keyword in the prompt..
Candidate Patterns
DP / Binary Search tails, Sliding Window, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
DP / Binary Search tails.
Supporting Data Structures
Depends on constraints.
Interview Justification
I would choose DP / Binary Search tails because The core property points toward DP / Binary Search tails, not just the loudest keyword in the prompt.. I would not choose Sliding Window because it does not match the property as directly.
Complexity
Usually O(n) with extra state, but verify constraints..
Reflection
What almost fools candidates is Sliding Window; the stronger signal is the property that supports DP / Binary Search tails..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Sliding Window
- 4.candidate refines by defending DP / Binary Search tails
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptSenior Problem 86: Design Twitter Feed. Return recent feed across followed users.
Interviewer review
Reader Worksheet
Signals
Design, Twitter, Feed.
Properties
The core property points toward Heap + HashMap design, not just the loudest keyword in the prompt..
Candidate Patterns
Heap + HashMap design, Sort all posts every request, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
Heap + HashMap design.
Supporting Data Structures
HashMap.
Interview Justification
I would choose Heap + HashMap design because The core property points toward Heap + HashMap design, not just the loudest keyword in the prompt.. I would not choose Sort all posts every request because it does not match the property as directly.
Complexity
Complexity depends on branching, heap size, or search range..
Reflection
What almost fools candidates is Sort all posts every request; the stronger signal is the property that supports Heap + HashMap design..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Sort all posts every request
- 4.candidate refines by defending Heap + HashMap design
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptSenior Problem 87: Minimum Cost to Connect Points. Connect all points with min total cost.
Interviewer review
Reader Worksheet
Signals
Minimum, Cost, to.
Properties
The core property points toward MST with Heap, not just the loudest keyword in the prompt..
Candidate Patterns
MST with Heap, DFS, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
MST with Heap.
Supporting Data Structures
Heap / Priority Queue.
Interview Justification
I would choose MST with Heap because The core property points toward MST with Heap, not just the loudest keyword in the prompt.. I would not choose DFS because it does not match the property as directly.
Complexity
Usually O(n) or O(n log n), depending on helper structure..
Reflection
What almost fools candidates is DFS; the stronger signal is the property that supports MST with Heap..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with DFS
- 4.candidate refines by defending MST with Heap
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptSenior Problem 88: Word Break II. Return all valid sentence segmentations.
Interviewer review
Reader Worksheet
Signals
Word, Break, II.
Properties
The core property points toward DP + Backtracking, not just the loudest keyword in the prompt..
Candidate Patterns
DP + Backtracking, Greedy, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
DP + Backtracking.
Supporting Data Structures
Depends on constraints.
Interview Justification
I would choose DP + Backtracking because The core property points toward DP + Backtracking, not just the loudest keyword in the prompt.. I would not choose Greedy because it does not match the property as directly.
Complexity
Usually O(n) with extra state, but verify constraints..
Reflection
What almost fools candidates is Greedy; the stronger signal is the property that supports DP + Backtracking..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Greedy
- 4.candidate refines by defending DP + Backtracking
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptSenior Problem 89: Regular Expression Matching. Match string with . and *.
Interviewer review
Reader Worksheet
Signals
Regular, Expression, Matching.
Properties
The core property points toward Dynamic Programming, not just the loudest keyword in the prompt..
Candidate Patterns
Dynamic Programming, Two Pointers, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
Dynamic Programming.
Supporting Data Structures
Depends on constraints.
Interview Justification
I would choose Dynamic Programming because The core property points toward Dynamic Programming, not just the loudest keyword in the prompt.. I would not choose Two Pointers because it does not match the property as directly.
Complexity
Complexity depends on branching, heap size, or search range..
Reflection
What almost fools candidates is Two Pointers; the stronger signal is the property that supports Dynamic Programming..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Two Pointers
- 4.candidate refines by defending Dynamic Programming
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptSenior Problem 90: Burst Balloons. Max coins from bursting balloons.
Interviewer review
Reader Worksheet
Signals
Burst, Balloons.
Properties
The core property points toward Interval DP, not just the loudest keyword in the prompt..
Candidate Patterns
Interval DP, Greedy, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
Interval DP.
Supporting Data Structures
Depends on constraints.
Interview Justification
I would choose Interval DP because The core property points toward Interval DP, not just the loudest keyword in the prompt.. I would not choose Greedy because it does not match the property as directly.
Complexity
Usually O(n) or O(n log n), depending on helper structure..
Reflection
What almost fools candidates is Greedy; the stronger signal is the property that supports Interval DP..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Greedy
- 4.candidate refines by defending Interval DP
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptSenior Problem 91: Sliding Puzzle. Minimum moves to solve 2x3 board.
Interviewer review
Reader Worksheet
Signals
Sliding, Puzzle.
Properties
The core property points toward BFS + visited, not just the loudest keyword in the prompt..
Candidate Patterns
BFS + visited, DFS, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
BFS + visited.
Supporting Data Structures
Queue / visited set.
Interview Justification
I would choose BFS + visited because The core property points toward BFS + visited, not just the loudest keyword in the prompt.. I would not choose DFS because it does not match the property as directly.
Complexity
Usually O(n) with extra state, but verify constraints..
Reflection
What almost fools candidates is DFS; the stronger signal is the property that supports BFS + visited..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with DFS
- 4.candidate refines by defending BFS + visited
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptSenior Problem 92: Autocomplete System. Suggest top historical sentences.
Interviewer review
Reader Worksheet
Signals
Autocomplete, System.
Properties
The core property points toward Trie + Heap/Sorting, not just the loudest keyword in the prompt..
Candidate Patterns
Trie + Heap/Sorting, HashMap only, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
Trie + Heap/Sorting.
Supporting Data Structures
Heap / Priority Queue.
Interview Justification
I would choose Trie + Heap/Sorting because The core property points toward Trie + Heap/Sorting, not just the loudest keyword in the prompt.. I would not choose HashMap only because it does not match the property as directly.
Complexity
Complexity depends on branching, heap size, or search range..
Reflection
What almost fools candidates is HashMap only; the stronger signal is the property that supports Trie + Heap/Sorting..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with HashMap only
- 4.candidate refines by defending Trie + Heap/Sorting
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptSenior Problem 93: Reconstruct Itinerary. Use all tickets in lexical order.
Interviewer review
Reader Worksheet
Signals
Reconstruct, Itinerary.
Properties
The core property points toward DFS Hierholzer + Heap/Sort, not just the loudest keyword in the prompt..
Candidate Patterns
DFS Hierholzer + Heap/Sort, BFS, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
DFS Hierholzer + Heap/Sort.
Supporting Data Structures
Stack / recursion.
Interview Justification
I would choose DFS Hierholzer + Heap/Sort because The core property points toward DFS Hierholzer + Heap/Sort, not just the loudest keyword in the prompt.. I would not choose BFS because it does not match the property as directly.
Complexity
Usually O(n) or O(n log n), depending on helper structure..
Reflection
What almost fools candidates is BFS; the stronger signal is the property that supports DFS Hierholzer + Heap/Sort..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with BFS
- 4.candidate refines by defending DFS Hierholzer + Heap/Sort
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptSenior Problem 94: Maximal Rectangle. Largest rectangle of 1s in matrix.
Interviewer review
Reader Worksheet
Signals
Maximal, Rectangle.
Properties
The core property points toward DP heights + stack, not just the loudest keyword in the prompt..
Candidate Patterns
DP heights + stack, BFS, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
DP heights + stack.
Supporting Data Structures
Depends on constraints.
Interview Justification
I would choose DP heights + stack because The core property points toward DP heights + stack, not just the loudest keyword in the prompt.. I would not choose BFS because it does not match the property as directly.
Complexity
Usually O(n) with extra state, but verify constraints..
Reflection
What almost fools candidates is BFS; the stronger signal is the property that supports DP heights + stack..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with BFS
- 4.candidate refines by defending DP heights + stack
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptSenior Problem 95: Russian Doll Envelopes. Max nested envelopes.
Interviewer review
Reader Worksheet
Signals
Russian, Doll, Envelopes.
Properties
The core property points toward Sorting + LIS Binary Search, not just the loudest keyword in the prompt..
Candidate Patterns
Sorting + LIS Binary Search, 2D DP brute force, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
Sorting + LIS Binary Search.
Supporting Data Structures
Depends on constraints.
Interview Justification
I would choose Sorting + LIS Binary Search because The core property points toward Sorting + LIS Binary Search, not just the loudest keyword in the prompt.. I would not choose 2D DP brute force because it does not match the property as directly.
Complexity
Complexity depends on branching, heap size, or search range..
Reflection
What almost fools candidates is 2D DP brute force; the stronger signal is the property that supports Sorting + LIS Binary Search..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with 2D DP brute force
- 4.candidate refines by defending Sorting + LIS Binary Search
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptSenior Problem 96: Expression Add Operators. Insert operators to reach target.
Interviewer review
Reader Worksheet
Signals
Expression, Add, Operators.
Properties
The core property points toward Backtracking, not just the loudest keyword in the prompt..
Candidate Patterns
Backtracking, DP only, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
Backtracking.
Supporting Data Structures
Depends on constraints.
Interview Justification
I would choose Backtracking because The core property points toward Backtracking, not just the loudest keyword in the prompt.. I would not choose DP only because it does not match the property as directly.
Complexity
Usually O(n) or O(n log n), depending on helper structure..
Reflection
What almost fools candidates is DP only; the stronger signal is the property that supports Backtracking..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with DP only
- 4.candidate refines by defending Backtracking
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptSenior Problem 97: Alien Dictionary with Invalid Prefix. Infer order or detect invalid dictionary.
Interviewer review
Reader Worksheet
Signals
Alien, Dictionary, with.
Properties
The core property points toward Graph + BFS/DFS, not just the loudest keyword in the prompt..
Candidate Patterns
Graph + BFS/DFS, Sorting, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
Graph + BFS/DFS.
Supporting Data Structures
Queue / visited set.
Interview Justification
I would choose Graph + BFS/DFS because The core property points toward Graph + BFS/DFS, not just the loudest keyword in the prompt.. I would not choose Sorting because it does not match the property as directly.
Complexity
Usually O(n) with extra state, but verify constraints..
Reflection
What almost fools candidates is Sorting; the stronger signal is the property that supports Graph + BFS/DFS..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Sorting
- 4.candidate refines by defending Graph + BFS/DFS
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptSenior Problem 98: Shortest Subarray With Sum at Least K. Find shortest subarray with sum at least K with negatives.
Interviewer review
Reader Worksheet
Signals
Shortest, Subarray, With.
Properties
The core property points toward Prefix Sum + Monotonic Deque, not just the loudest keyword in the prompt..
Candidate Patterns
Prefix Sum + Monotonic Deque, Sliding Window, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
Prefix Sum + Monotonic Deque.
Supporting Data Structures
Depends on constraints.
Interview Justification
I would choose Prefix Sum + Monotonic Deque because The core property points toward Prefix Sum + Monotonic Deque, not just the loudest keyword in the prompt.. I would not choose Sliding Window because it does not match the property as directly.
Complexity
Complexity depends on branching, heap size, or search range..
Reflection
What almost fools candidates is Sliding Window; the stronger signal is the property that supports Prefix Sum + Monotonic Deque..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Sliding Window
- 4.candidate refines by defending Prefix Sum + Monotonic Deque
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptSenior Problem 99: Find Median in Data Stream at Scale. Support streaming inserts and median queries.
Interviewer review
Reader Worksheet
Signals
Find, Median, in.
Properties
The core property points toward Two Heaps, not just the loudest keyword in the prompt..
Candidate Patterns
Two Heaps, Sort all data, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
Two Heaps.
Supporting Data Structures
Heap / Priority Queue.
Interview Justification
I would choose Two Heaps because The core property points toward Two Heaps, not just the loudest keyword in the prompt.. I would not choose Sort all data because it does not match the property as directly.
Complexity
Usually O(n) or O(n log n), depending on helper structure..
Reflection
What almost fools candidates is Sort all data; the stronger signal is the property that supports Two Heaps..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Sort all data
- 4.candidate refines by defending Two Heaps
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Problem promptSenior Problem 100: Serialize N-ary Tree. Serialize and deserialize an N-ary tree.
Interviewer review
Reader Worksheet
Signals
Serialize, N-ary, Tree.
Properties
The core property points toward DFS/BFS with child counts, not just the loudest keyword in the prompt..
Candidate Patterns
DFS/BFS with child counts, Binary tree assumptions, brute force.
Verify Assumptions
The stated constraints preserve the property used by the chosen pattern..
Chosen Pattern
DFS/BFS with child counts.
Supporting Data Structures
Queue / visited set.
Interview Justification
I would choose DFS/BFS with child counts because The core property points toward DFS/BFS with child counts, not just the loudest keyword in the prompt.. I would not choose Binary tree assumptions because it does not match the property as directly.
Complexity
Usually O(n) with extra state, but verify constraints..
Reflection
What almost fools candidates is Binary tree assumptions; the stronger signal is the property that supports DFS/BFS with child counts..
Interview Mode
- 1.Interviewer asks for the first instinct
- 2.candidate names signals
- 3.interviewer challenges with Binary tree assumptions
- 4.candidate refines by defending DFS/BFS with child counts
- 5.expert feedback: Interview-ready if the candidate rejects the tempting alternative out loud..
Interviewer's Verdict
Pattern Recognition
5/5
Reasoning
5/5
Assumption Verification
4/5
Communication
5/5
Algorithm Choice
5/5
Complexity Discussion 4/5.
Complexity Discussion 4/5.
Interview room
How the Conversation Sounds
Bad
“Interviewer: Why this pattern? Candidate: I have seen this problem before.”
Good
“Interviewer: Why this pattern? Candidate: The key property is repeated range computation, so Prefix Sum removes the repeated work.”
Manager
“Interviewer: Why not the obvious keyword pattern? Candidate: That keyword is misleading because the assumption behind that pattern does not hold.”
SeniorEngineer
“Interviewer: What if this constraint changes? Candidate: I would switch patterns because the current proof depends on that constraint.”
Leadership
“Interviewer: What are you optimizing for? Candidate: Correctness first, then the simplest complexity improvement justified by the properties.”
Short answers
Frequently Asked Questions
No. It is a capstone practice workbook. Use the individual articles for deeper pattern explanations and this workbook for mixed interview reasoning.
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