3. 无重复字符的最长子串

class Solution:
    def lengthOfLongestSubstring(self, s: str) -> int:
        res = 0
        visited = list()
        for i in range(len(s)):
            # 左移窗口
            while s[i] in visited: visited.pop(0)
            # 右移窗口
            visited.append(s[i])
            res = max(res, len(visited))
        return res