424. Longest Repeating Character Replacement

https://leetcode.com/problems/longest-repeating-character-replacement/

Python

class Solution:
    def characterReplacement(self, s: str, k: int) -> int:
        letters = set(s)
        max_length = 0

        for letter in letters:
            left, count = 0, 0

            for right in range(len(s)):
                if s[right] == letter:
                    count += 1

                # All letters which needs to be replaced can't large than k
                # If its larger, move the left forward
                while right-left+1 - count > k:
                    if s[left] == letter:
                        count -= 1
                    left += 1

                max_length = max(max_length, right-left+1)

        return max_length