无重复字符的最长子串

class Solution:
    def lengthOfLongestSubstring(self, s: str) -> int:
        res, right = 0, 0
        visit = set()
        for i in range(len(s)):
            if i > 0:
                visit.remove(s[i - 1])
            while right < len(s) and s[right] not in visit:
                visit.add(s[right])
                right += 1
                res = max(res, right - i)
        return res