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LeetCode 3 Longest Substring Without Repeating Characters is one of the top five most asked questions at Meta and Amazon. Master the variable sliding window with a hash map to solve it in O(n) time and O(min n,m) space.
LeetCode 424 — a classic FAANG sliding window problem (Google, Microsoft, Amazon). Master the max-frequency invariant that powers the optimal O(n) solution.
LeetCode 567 — detect if any permutation of s1 appears as a substring of s2 using a fixed-size sliding window. Frequently asked at Google, Amazon, and Microsoft.
LeetCode 904 — find the longest contiguous subarray with at most two distinct values. A reskinned classic that appears in Google, Amazon, and Microsoft interviews.
LeetCode 1695 — find the maximum sum of a subarray with all unique values using a HashSet sliding window. A favorite at Google and Amazon for testing window invariants.