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LeetCode 41 — asked at Amazon, Google, and Microsoft. Find the smallest missing positive integer in O(n) time and O(1) space. Use the array itself as a hash map: place each number i at index i-1, then scan for the first mismatch. The answer must be in [1, n+1].
LeetCode 84 — asked at Amazon, Google, and Microsoft. Find the largest rectangle in a histogram using a monotonic increasing stack. For each bar, find the nearest shorter bars on both sides to compute the maximum width. O(n) time, O(n) space.
Master LeetCode 76 — the gold-standard Hard sliding window problem asked at Google, Meta, and Amazon. Learn the "formed" counter trick that reduces window validity checks from O(|t|) to O(1), trace through a full dry run, and avoid the five bugs that most often break this one.
Master LeetCode 315 — one of the most common FAANG hard problems. Learn why a naive O(n²) scan fails at scale, how merge sort secretly counts inversions as a side effect, and how to trace through every swap on paper. Includes both brute-force and optimal solutions in Python and JavaScript, a full complexity table, and the three follow-up problems that frequently appear in the next interview round.
LeetCode 4 is one of the most feared Hard problems in FAANG interviews. Learn exactly why the partition insight works, trace through a full binary search dry run, understand the five common bugs that cause silent wrong answers, and walk away with production-quality Python and JavaScript solutions.