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LeetCode 1234 Replace the Substring for Balanced String is asked at Google and Amazon. Find the minimum window to replace in O(n) using a shrinkable sliding window over QWER frequencies.
LC 1888 asks for the minimum flips to make a binary string alternating after any rotations. Double the string and slide a fixed window of size n against both target patterns — the canonical circular sliding window trick.
LC 1456 asks for the maximum vowels in any substring of length k. A canonical fixed-size sliding window — add the new right character, subtract the departing left character, track the running max. O(n) time, O(1) space.
LC 1151 asks for minimum swaps to group all 1s in a circular binary array. Count total 1s to set the window size, then maximize 1s inside any window position using modulo indexing. O(n) time, O(1) space.
LC 2516 asks for the minimum minutes to collect at least k of each character from a string's ends. Flip it: find the longest middle window you can skip so the outside has enough of each character. O(n) time, O(1) space.