[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.

Hint:
找出字符串里面最大的不重复的（连续的，不能跳），返回为ans，left指示，i开始遍历字符串，判断条件是s[i] in last and last[s[i]] >= left: 满足这个条件，left = last[s[i]]+1，否则last[s[i]] = i，给出的是max（ans， i-left+1）

Code:

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