Leetcode 3. Longest Substring without repeating characters

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.

 

思路：类似双指针，用left标定以当前字母结尾的最长无重的substring的起点。逐个扫描字母，如果这个字母当前的substring里面没有，那么当前的substring长度就可以加一。如果这个字母已经在substring里面了，例如：

当扫描到第二个c的时候，left应该移到d上来。并且应该将 C:2 更新为 C:6。 这里由于需要第一个c 的index，应该使用一个hash table。 如果cur后面又出现了一个a，由于目前a这个key的value小于left，所以说明current non repeating substring里面没有a。注意L14的条件。

class Solution(object):
    def lengthOfLongestSubstring(self, s):
        """
        :type s: str
        :rtype: int
        """
        
        ans = 0
        left = 0
        
        curStr = {}
        
        for i in range(len(s)):
            if s[i] in curStr and curStr[s[i]] >= left:
                left = curStr[s[i]] + 1
            
            curStr[s[i]] = i
            
            ans = max(ans, i-left +1)
        
        return ans