1208. 尽可能使字符串相等

class Solution:
    def equalSubstring(self, s: str, t: str, maxCost: int) -> int:
        start = 0
        end = 0
        ans = 0
        res = 0
        while end < len(s) and start < len(s):
            ans = ans + abs(ord(s[end])-ord(t[end]))
            if ans > maxCost:
                ans = ans - abs(ord(s[start])-ord(t[start]))
                start = start + 1
                end = end + 1
            else:
                end = end + 1
            res = max(res, end-start)
        return res