原题
1 class Solution: 2 def lengthOfLongestSubstring(self, s: str) -> int: 3 ans = left = 0 4 dic = {} 5 for i,c in enumerate(s): 6 if c in dic: 7 left = max(left,dic[c] + 1) 8 ans = max(ans,i - left + 1) 9 dic[c] = i 10 return ans