LeetCode---Longest Substring Without Repeating Characters

Given a string, find the length of the longest substring without repeating characters.

给定一个字符串，在不重复字符的情况下找出最长子字符串的长度

Example 1:

Input: "abcabcbb"
Output: 3 
Explanation: The answer is "abc", with the length of 3. 

Example 2:

Input: "bbbbb"
Output: 1
Explanation: The answer is "b", with the length of 1.

Example 3:

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.

题目就是要求找出最长的无重复子串

可以采用滑动窗口的方法，用i和j分别指向窗口的前后下界，如果当前字符未出现在窗口，j后移，如果出现了，i后移。窗口用集合实现，判存复杂度为O(1)。总的时间复杂度为O(2n)=O(n)，最坏情况为每个字符都被访问两遍(分别作为窗口的头尾)，空间复杂度为O(k)

class Solution:
    def lengthOfLongestSubstring(self, s):
        L=len(s)
        if L==0:
            return 0
        i=j=0
        chardict=set()
        maxlen=0
        
        while i