📝 Interview Walkthroughs

A step-by-step walkthrough of Best Time to Buy and Sell Stock as it unfolds in a real coding interview. Learn the greedy O(n) approach, common mistakes, and how strong candidates communicate the solution.

How to solve Contains Duplicate (LeetCode #217) in a coding interview. Covers hash set vs. sorting trade-offs, early exit optimization, the follow-up question, and what interviewers are really testing.

Master Longest Palindrome for your coding interview. Learn the pairs-plus-center greedy pattern, frequency counting, and what interviewers actually evaluate.

How to solve Majority Element (LeetCode #169) in a coding interview. Covers hash map, sorting, and Boyer-Moore Voting Algorithm approaches with the cancellation intuition explained clearly.

Master Meeting Rooms for your coding interview. Learn the sort-then-scan interval pattern, overlap detection, and what interviewers actually evaluate.

Master Ransom Note for your coding interview. Learn character frequency counting, the 26-element array optimization, and what interviewers actually evaluate.

A step-by-step walkthrough of the Two Sum problem as it unfolds in a real coding interview. Learn the optimal hash map approach, common mistakes, and how strong candidates communicate their solution.

A step-by-step guide to solving the 3Sum problem in a coding interview: brute force to optimal O(n²) with sorting, two pointers, and duplicate handling explained clearly.

A step-by-step walkthrough of LeetCode #11 as it plays out in a real coding interview. Learn the two-pointer technique, the greedy argument for why it's correct, and the proof that moving the shorter pointer never misses the optimal pair.

Master Find All Anagrams in a String for your coding interview. Learn the fixed-size sliding window, the matches counter optimization, and what interviewers actually evaluate.

Master Insert Interval for your coding interview. Learn the three-case linear scan, merge boundary conditions, and what interviewers actually evaluate.

Master K Closest Points to Origin for your coding interview. Learn the max-heap approach, Quickselect, why sqrt is unnecessary, and what interviewers actually evaluate.

A step-by-step guide to solving Maximum Subarray in a coding interview: Kadane's algorithm, the greedy reset decision, the DP framing, all-negative edge cases, and the follow-up questions interviewers use to probe depth.

A step-by-step walkthrough of the Merge Intervals problem as it unfolds in a real coding interview. Learn the optimal approach, common mistakes, and how strong candidates communicate their solution.

A step-by-step walkthrough of LeetCode #238 as it unfolds in a real coding interview. Learn the prefix/suffix product technique, the O(1) space optimization, and the edge cases that catch even prepared candidates.

Master Sort Colors for your coding interview. Learn the Dutch National Flag algorithm, three-pointer invariants, and what interviewers actually evaluate.

Master Spiral Matrix for your coding interview. Learn boundary-shrinking traversal, edge cases for non-square matrices, and what interviewers actually evaluate.

A step-by-step walkthrough of the Task Scheduler problem as it unfolds in a real coding interview. Learn the greedy formula approach, the heap-based simulation alternative, and how strong candidates derive the scheduling formula from first principles.

A step-by-step walkthrough of the Find Median from Data Stream problem as it unfolds in a real coding interview. Learn the two-heap approach, the rebalancing invariant, and how to simulate a max-heap in Python.

A step-by-step guide to solving Trapping Rain Water in a coding interview: the geometric insight, prefix/suffix arrays, and the two-pointer O(1) space technique explained clearly.

A step-by-step guide to solving Linked List Cycle in a coding interview: Floyd's tortoise and hare algorithm, the hash set baseline, the mathematical proof of why pointers meet, and what strong candidates sound like.

A step-by-step guide to solving Merge Two Sorted Lists in a coding interview: the dummy node pattern, iterative and recursive approaches, pointer mistakes to avoid, and what strong candidates sound like.

Master Middle of the Linked List for your coding interview. Learn the fast-slow pointer pattern, even-length list handling, and what interviewers actually evaluate.

A step-by-step guide to solving Reverse Linked List in a coding interview: the three-pointer iterative technique, the recursive approach, pointer mistakes to avoid, and what strong candidates sound like.

A step-by-step guide to solving LRU Cache in a coding interview: from naive lists to the optimal hash map + doubly linked list design, with pointer operations and sentinel nodes explained.

A step-by-step walkthrough of LeetCode #23 as it plays out in a real coding interview. Learn the min-heap K-way merge pattern, the Python tiebreaker trick, and the divide-and-conquer alternative that uses O(1) extra space.

A step-by-step walkthrough of the Balanced Binary Tree problem as it unfolds in a real coding interview. Learn the O(n²) trap, the bottom-up sentinel technique, and how strong candidates avoid redundant work.

Master Diameter of Binary Tree for your coding interview. Learn the DFS-with-side-effect pattern, why the path may not pass through root, common mistakes, and what interviewers evaluate.

A step-by-step guide to solving Invert Binary Tree in a coding interview: recursive and iterative approaches, tree traversal reasoning, edge cases, and what strong candidates sound like.

Master Lowest Common Ancestor of a BST for your coding interview. Learn the split-point insight, iterative O(1) solution, and what interviewers actually evaluate.

Master Maximum Depth of Binary Tree for your coding interview. Learn recursive DFS, iterative BFS, common mistakes, and what interviewers actually evaluate.

A step-by-step guide to solving Binary Tree Level Order Traversal in a coding interview. Learn the BFS queue-snapshot pattern, common mistakes, and what interviewers actually score you on.

How to solve Binary Tree Right Side View (LeetCode #199) in a coding interview using BFS level-order traversal. Includes both BFS and DFS approaches, complexity analysis, common mistakes, and interview dialogue.

A step-by-step walkthrough of Construct Binary Tree from Preorder and Inorder Traversal as it unfolds in a real coding interview. Learn the recursive reconstruction algorithm, the hash map optimization, and how to avoid common index-tracking mistakes.

Master Kth Smallest Element in a BST for your coding interview. Learn the in-order traversal shortcut, iterative early-exit, and the augmented-tree follow-up.

A step-by-step walkthrough of LeetCode #236 as it plays out in a real coding interview. Learn the single-pass postorder DFS approach, why BST solutions don't work here, and how to handle the self-ancestor edge case.

A step-by-step walkthrough of LeetCode #98 as it plays out in a real coding interview. Learn the bounds-propagation technique, why the naive local-check approach fails, and the edge cases that catch even experienced candidates.

A step-by-step walkthrough of Serialize and Deserialize Binary Tree as it unfolds in a real coding interview. Learn both BFS and DFS approaches, how to encode null nodes, and why the DFS preorder solution is the cleanest interview implementation.

Master Flood Fill for your coding interview. Learn the grid DFS/BFS pattern, boundary handling, infinite loop prevention, and what interviewers actually evaluate.

A step-by-step walkthrough of the 01 Matrix problem as it unfolds in a real coding interview. Learn multi-source BFS, why seeding from zeros beats seeding from ones, and how strong candidates explain the approach.

A step-by-step walkthrough of the Accounts Merge problem as it unfolds in a real coding interview. Learn the Union-Find approach, why name-based merging fails, and how to reconstruct sorted email groups.

Master Clone Graph for your coding interview. Learn the DFS clone-map pattern, cycle handling, and what interviewers actually evaluate.

A step-by-step guide to solving Course Schedule in a coding interview. Learn DFS three-state cycle detection on directed graphs, common mistakes, and what interviewers actually score you on.

A step-by-step walkthrough of the Minimum Height Trees problem as it unfolds in a real coding interview. Learn the leaf-trimming algorithm, why MHT roots are always the tree's center nodes, and how to implement the solution in O(n).

A step-by-step guide to solving Number of Islands in a coding interview: grid-as-graph modeling, DFS vs BFS tradeoffs, in-place marking, and complexity analysis explained clearly.

Master Rotting Oranges for your coding interview. Learn multi-source BFS, layer-by-layer traversal, and what interviewers actually evaluate.

A step-by-step walkthrough of the Word Ladder problem as it unfolds in a real coding interview. Learn why BFS is the right tool, the neighbor-generation trick, and how bidirectional BFS cuts the search space.

A step-by-step walkthrough of the Climbing Stairs problem as it unfolds in a real coding interview. Learn the full recursion-to-DP progression, the Fibonacci connection, and how strong candidates communicate their optimization steps.

A step-by-step guide to solving the Coin Change problem in a coding interview: from recursive brute force to optimal bottom-up DP with recurrence derivation and greedy failure analysis.

How to solve Partition Equal Subset Sum (LeetCode #416) in a coding interview using 0/1 knapsack DP. Covers the key reduction, space-optimized 1D DP, reverse iteration insight, and common mistakes.

Master Unique Paths for your coding interview. Learn the 2D DP recurrence, 1D space optimization, the combinatorics shortcut, and what interviewers actually evaluate.

A step-by-step walkthrough of LeetCode #139 as it plays out in a real coding interview. Learn the DP recurrence, why naive recursion explodes exponentially, and the base case that trips up most candidates.

A step-by-step walkthrough of the Maximum Profit in Job Scheduling problem as it unfolds in a real coding interview. Learn the DP + binary search approach, the sorting prerequisite, and how to implement the clean dp-array pattern.

A step-by-step walkthrough of the Add Binary problem as it unfolds in a real coding interview. Learn the right-to-left pointer technique, carry propagation, and how strong candidates handle unequal-length strings.

How to solve Valid Anagram (LeetCode #242) in a coding interview. Covers frequency counting vs. sorting, the Unicode follow-up, edge cases, and what strong candidates say to stand out.

Master Valid Palindrome for your coding interview. Learn the two-pointer approach, O(1) space optimization, common mistakes, and what interviewers actually evaluate.

A step-by-step walkthrough of LeetCode #5 as it plays out in a real coding interview. Learn the expand-around-center technique, why brute force fails at scale, and the odd-vs-even center distinction that trips up most candidates.

A step-by-step walkthrough of LeetCode #3 as it unfolds in a real coding interview. Learn the sliding window approach, the critical index-tracking guard, and how strong candidates communicate their solution.

A step-by-step walkthrough of the String to Integer (atoi) problem as it unfolds in a real coding interview. Learn to enumerate edge cases upfront, handle overflow clamping, and write a clean single-pass parser.

A step-by-step walkthrough of LeetCode #76 as it plays out in a real coding interview. Learn the two-phase sliding window, the formed counter that makes validity O(1), and the frequency map design that handles duplicate characters correctly.

Master Implement Queue using Stacks for your coding interview. Learn the two-stack inbox/outbox pattern, amortized O(1) reasoning, and what interviewers actually evaluate.

Master Min Stack for your coding interview. Learn the auxiliary-state pattern for O(1) getMin, two implementation approaches, and what interviewers actually evaluate.

A step-by-step guide to solving Valid Parentheses in a coding interview: stack-based reasoning, bracket matching with hash maps, edge cases, and what strong candidates sound like.

Master Evaluate Reverse Polish Notation for your coding interview. Learn the stack-based evaluation pattern, Python division truncation, and what interviewers actually evaluate.

A step-by-step walkthrough of the Basic Calculator problem as it unfolds in a real coding interview. Learn the stack-save pattern for nested parentheses, sign context management, and how strong candidates trace through expressions.

A step-by-step walkthrough of the Largest Rectangle in Histogram problem as it unfolds in a real coding interview. Learn the monotonic stack approach, the sentinel trick, and how to correctly compute rectangle widths.

A step-by-step walkthrough of the Binary Search problem as it unfolds in a real coding interview. Learn the precise boundary logic, off-by-one traps, and how strong candidates communicate this deceptively simple algorithm.

Master First Bad Version for your coding interview. Learn the monotonic binary search pattern, overflow-safe midpoint, common off-by-one mistakes, and what interviewers evaluate.

A step-by-step walkthrough of LeetCode #33 as it plays out in a real coding interview. Learn how to adapt binary search for rotated arrays, nail the boundary conditions, and handle the follow-ups interviewers use to test depth.

A step-by-step walkthrough of the Time Based Key-Value Store problem as it unfolds in a real coding interview. Learn the optimal approach using binary search on sorted timestamps, common mistakes, and how strong candidates communicate their solution.

A step-by-step walkthrough of LeetCode #208 as it unfolds in a real coding interview. Learn how to design a Trie from scratch, explain node structure clearly, and avoid the is_end flag mistake that catches most candidates.

A step-by-step walkthrough of LeetCode #39 as it plays out in a real coding interview. Learn the backtracking decision tree, the choose/explore/unchoose pattern, and the pruning techniques that separate clean solutions from broken ones.

Master Letter Combinations of a Phone Number for your coding interview. Learn the backtracking Cartesian product pattern, the BFS alternative, and what interviewers actually evaluate.

A step-by-step walkthrough of LeetCode #46 as it plays out in a real coding interview. Learn the used-array backtracking pattern, why it differs from combination problems, and the swap-based alternative that saves space.

Master Subsets for your coding interview. Learn the backtracking snapshot pattern, the recursion tree, and what interviewers actually evaluate.

Master Word Search for your coding interview. Learn the grid DFS + backtracking pattern, in-place visited marking, and what interviewers actually evaluate.