LeetCode 3. Longest Substring Without Repeating Characters---Python实现

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

Examples:

Given 

"abcabcbb"

, the answer is 

"abc"

,
which the length is 3.

Given "bbbbb", the answer is 

"b"

,
with the length of 1.

Given 

"pwwkew"

, 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.

题意很明白，在一个字符串中找一个最长的不重复连续字串，选用一个字典来存储每个字符的位置，进行遍历即可。具体代码分析如下。class Solution(object):
    def lengthOfLongestSubstring(self, s):
        """
        :type s: str
        :rtype: int
        """
        usechar={}
        start=length=0 # /length=i=0
        for i in range(len(s)):  # for i in len(s):
            if s[i] in usechar and start <=usechar[s[i]]:  # if s[i] in usechar and start<=s[i]:
                start=usechar[s[i]]+1# start=s[i]+1 #直接从重复的之后再来算啊。usechar里面的都是唯一的啊。
            else:
                length=max(length,i-start+1)
            usechar[s[i]]=i;
        return length