424. 替换后的最长重复字符

class Solution:
    def characterReplacement(self, s: str, k: int) -> int:
        left =0 
        right =0 
        result=0 
        character_cnt= {}
        max_freq =0 
        while right<len(s):
            character_cnt[s[right]] = character_cnt.get(s[right], 0) + 1

            max_freq =max(max_freq,character_cnt[s[right]])
            while  (right-left+1 -max_freq) > k  :
                character_cnt[s[left]]-=1
                left +=1

            result = max(result,right-left+1)
            right +=1 
        return result