python错误小计：if错误，应当改为while

使用滑动窗口计算无重复字符的最长子串：https://leetcode-cn.com/problems/longest-substring-without-repeating-characters/solution/hua-dong-chuang-kou-by-powcai/

 def lengthOfLongestSubstring(self, s: str) -> int:
            if not s:
                return 0
            left = 0
            max_len, cur_len = 0, 0
            temp_set = set()
            n = len(s)
            for i in range(n):
                cur_len += 1
                if s[i] in temp_set:
                    temp_set.remove(s[left])
                    left += 1
                    cur_len -= 1
                max_len = max(max_len, cur_len)
                temp_set.add(s[i])
            return max_len

其中if错误，应当改为while

def lengthOfLongestSubstring(self, s: str) -> int:
    if not s:return 0
    left = 0
    lookup = set()
    n = len(s)
    max_len = 0
    cur_len = 0
    for i in range(n):
        cur_len += 1
        while s[i] in lookup:
            lookup.remove(s[left])
            left += 1
            cur_len -= 1
        if cur_len > max_len:max_len = cur_len
        max_len = max(max_len, cur_len)
        lookup.add(s[i])
    return max_len