分类：HashTable
考察知识点：HashTable String
最优解时间复杂度：O(n)
3. Longest Substring Without Repeating Characters
Given a string, find the length of the longest substring without repeating characters.
Example1:
Input: "abcabcbb"
Output: 3
Explanation: The answer is "abc", with the length of 3.
Example2:
Input: "bbbbb"
Output: 1
Explanation: The answer is "b", with the length of 1.
Example2:
Input: "pwwkew"
Output: 3
Explanation: The answer is "wke", with the length of 3.
Note that the answer must be a substring, "pwke" is a subsequence and not a substring.
代码：
解法:
class Solution:
def lengthOfLongestSubstring(self, s: str) -> int:
length = 0
if s==None or s=="":
return length
start = 0
char_dict = dict()
for end in range(len(s)):
if s[end] in char_dict:
# 找最长的不重复字符的字符串
start = max(start, char_dict[s[end]]+1)
char_dict[s[end]] = end
# 找这些字符串里最大的
length = max(length, end-start+1)
return length
讨论：
1.看到Without repeatedly啥的，记得用Hash Table，在Python中就是dictionary
2.j是新的一段的开头，一定要记住** j=max(j,d[n]+1)**,不能让它回到前面去
WechatIMG1626.jpeg
