1582 articles
LeetCode 238 is one of the most frequently asked medium problems at Google and Meta. Learn why the no-division constraint is intentional, how the prefix × suffix insight unlocks the O(n) solution, and how a single running variable eliminates the extra O(n) space entirely.
Master the classic Merge Intervals problem (LeetCode 56) asked at Google, Meta, Amazon, and Microsoft. Learn why sorting by start time is the key insight, the exact overlap condition (c ≤ b), a step-by-step visual dry run, 4 common mistakes, Python and JavaScript solutions, and follow-up problems including Insert Interval, Non-overlapping Intervals, and Meeting Rooms II.
Traverse an m×n matrix in spiral order. Master the boundary-shrinking technique — maintain top, bottom, left, right walls and peel layer by layer. Covers edge cases, visual dry run, common bugs, Python & JavaScript solutions, and follow-ups like Spiral Matrix II.
Group strings that are anagrams of each other using two canonical approaches: sorted string key O(n·k·log k) and character frequency tuple key O(n·k). Understand when the difference matters, trace through a dry run, dodge the common traps, and leave any interview with both solutions ready to go.
Master LeetCode 3 — the canonical sliding window problem. Understand the "shrink from left" insight, the critical stale-index bug with max(), and both set-based and hashmap-optimized solutions in Python and JavaScript. Includes a full step-by-step dry run and follow-up problems LC 340 and LC 159.