272B - Dima and Sequence - CodeForces Solution

#include<iostream>
#include<map>
using namespace std;
#define int long long int
signed  main()
{
        int n;
        cin>>n;
        map<int,int>mp;
        for(int i=0;i<n;i++){
                int x;
                cin>>x;
                int ans=0;
                while(x){
                        ans+=x%2;
                        x/=2;
                }
                mp[ans]++;
        }
        int ans=0;
        for(auto x:mp){
                ans+=(x.second)*(x.second-1)/2;
        }
        cout<<ans<<endl;
return 0;
}