leetcode_longest_substring_without_repeating_characters

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难度：Medium

每次维护以当前字符串结尾的不重复字符串的长度。一个hashset，存放之前的元素。

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class Solution {
public:
    int lengthOfLongestSubstring(string s) {
        if(s.size()==0) return 0;
        unordered_set<char> char_set;
        int max_len = 1;
        int start_index = 0;
        char_set.insert(s[0]);
        for(int i = 1; i < s.size(); i++)
        {
            while(char_set.count(s[i]) != 0 && !char_set.empty())
            {
                char_set.erase(s[start_index++]);
            }
            char_set.insert(s[i]);
            max_len = max(max_len, i-start_index+1);
        }
        return max_len;
    }
};