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Longest Repeating Character Replacement

advancedlayer B5 · Sliding window5 tests

You are given a string s of uppercase letters and an integer k. You may pick at most k positions and change each to any letter you like. Return the length of the longest substring that can be made of a single repeated character afterwards.

  • You do not have to use all k changes
  • s may be empty, in which case the answer is 0
  • Aim for a single O(n) pass — no re-scanning the window

Example: with s = "AABABBA" and k = 1 the answer is 4 (change one character to turn "ABBA" into "BBBB").

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