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.

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主要考察字符串中的最大子串。

思路很简单：

1，由于需要判重并且记录索引，所以这里采用hashmap

2，一个字符串中无重的子串可能不止一个，要求得最大子串的长度，肯定需要max函数来不断更新最大值

3，从头开始，依次遍历字符串，并记录子串长度，同时更新子串最大值，若子串达到极限且字符串未到末尾，确定下一个子串的开始位置，并重新计算长度

class Solution(object):    def lengthOfLongestSubstring(self, s):        """        :type s: str        :rtype: int        """        start = 0        maxlen = 0        dic = {}        for i in range(len(s)):            if s[i] in dic and start<=dic[s[i]]:                start = dic[s[i]] + 1            else:                maxlen = max(maxlen, i-start+1)            dic[s[i]] = i        return maxlen

确定新子串的开始位置是本题的难点。