题目：

class Solution:def lengthOfLongestSubstring(self, s):if s:resultList=[]length=[]item=0i=0while i<len(s):if s[i] in resultList:resultList.clear()i=item+1item=iresultList.append(s[i])length.append(len(resultList))i+=1return max(length)return 0

从后往前

class Solution:def lengthOfLongestSubstring(self, s: str) -> int:if s == '':return 0if len(s) == 1:return 1def find_left(s, i):tmp_str = s[i]j = i - 1while j >= 0 and s[j] not in tmp_str:tmp_str += s[j]j -= 1return len(tmp_str)length = 0for i in range(0, len(s)):length = max(length, find_left(s, i))return length

700ms

哈希

class Solution:def lengthOfLongestSubstring(self, s):ans=0left=0right=0hashset=set([])n=len(s)while left<n:while right<n and s[right] not in hashset:hashset.add(s[right])ans=max(ans,right-left+1)right+=1hashset.remove(s[left])left+=1if n-left <ans:breakreturn ans