Longest Repeating Character Replacement

The unmodified LeetCode 424 prompt: replace at most `k` characters in an uppercase string and return the longest substring that can be made entirely one repeated character. Requirements Given an uppercase English string s and an integer k, choose a substring. Within that substring, replace at most k characters with any uppercase English letter. Return the maximum possible substring length whose characters can all be made identical. Examples Input: s = "ABAB", k = 2 Output: 4 Input: s = "AABABBA", k = 1 Output: 4 Notes The prompt was the unmodified LC 424 problem. The round began with a resume drill and a question about how an LLM could be applied to the team's existing system. The coding portion was completed quickly within a 45-minute interview. Preparation Derive the window-validity condition in terms of window length, the most frequent character, and the replacement budget. Practice explaining why the tracked maximum frequency does not need to decrease on every left-boundary move. Test k = 0, an all-identical string, alternating characters, and a budget larger than the string.