最长无重复字符子串长度
维护两个指针pos_l和pos_r，每次pos_r右移一位，如果该字符在pos_l~pos_r-1之间已经出现过，则更新该字符最后出现的位置，同时pos_l右移一位，否则，更新最长无重复字符子串长度
一开始没想清楚pos_l的更新，WA*4
1 #3
2 #Runtime: 108 ms
3 #Memory Usage: 13.5 MB
4
5 class Solution(object):
6 def lengthOfLongestSubstring(self, s):
7 """
8 :type s: str
9 :rtype: int
10 """
11 dict_s = {}
12 pos_l = 0
13 pos_r = 0
14 ans = 0
15 while pos_r < len(s):
16 if s[pos_r] in dict_s:
17 if dict_s[s[pos_r]] >= pos_l:
18 pos_l = dict_s[s[pos_r]] + 1
19 dict_s[s[pos_r]] = pos_r
20 else:
21 dict_s[s[pos_r]] = pos_r
22 ans = max(ans, pos_r - pos_l + 1)
23 pos_r += 1
24 return ans