class Solution {
public:
    int longestSubstringWithoutDuplication(string s) {
        unordered_map<char, int> hash;
        int res = 0;
        for (int i = 0, j = 0; j < s.size(); j ++ )
        {
            hash[s[j]] ++ ;
            while (hash[s[j]] > 1) hash[s[i ++ ]] -- ;

            res = max(res, j - i + 1);
        }
        return res;
    }
};