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