int compress(vector<char>& chars)  
    { 
        map<char,int> mp; 
        for(int i = 0; i<chars.size(); i++) 
        { 
            mp[chars[i]]++; 
        }  
        vector<int> vect; 
        for(auto x:mp) 
        { 
            if(x.second==1) 
            { 
                 
                 vect.push_back(x.first); 
            } 
            else 
            { 
                vect.push_back(x.first); 
                vect.push_back(x.second); 
            } 
        }   
        for(auto it:vect) 
        cout<<it<<" "; 
    }