class Solution {
    std::unordered_map<char,int> um;
public:
    int lengthOfLongestSubstring(string s) {
        int left=0;
        int right=0;
        int maxvalue=0;
        int val=0;
        while(right<s.size()){
            auto res=um.find(s[right]);
            if(um.end()!=res){
                while(left<=right&&left<=res->second){
                    um.erase(s[left]);
                    left++;
                    val--;
                }
            }
            um.insert(std::make_pair(s[right],right));
            right++;
            val++;
            maxvalue=maxvalue>val?maxvalue:val;
        }
        return maxvalue;
        
    }
};