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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class Solution {public:    int lengthOfLongestSubstring(string s) {        int length = 0;        int start  = -1;        unordered_map<char, int> cmap;//记录字符串s中的字符以及位置        unordered_map<char, int>::iterator map_iter;        for(int i = 0; i!=s.length();++i)        {            map_iter=cmap.find(s[i]);//遍历字符串s,在cmap中寻找字符s[i]            if(map_iter!=cmap.end())//遍历过程中出现重复字符时，将当前字符的位置更新为子字符串长度的计算起点，计算子字符串的长度            {                if(map_iter->second>start) start = map_iter->second;                cmap.erase(map_iter);            }//if            cmap.insert(make_pair(s[i],i));            length = max(length,i - start);//更新子字符串长度        }//for        return length;    }};