Sort by Set Bit Count

// { Driver Code Starts
#include <bits/stdc++.h>
using namespace std;


 // } Driver Code Ends

This question is now solved.......................
/*
bool compare(int a,int b){
    int ca=0,cb=0;
    while(a){
        if(a&1)ca++;
        a=a>>1;
    }
    while(b){
        if(b&1)cb++;
        b=b>>1;
    }
    return ca>cb;
}
*/
int countBits(int a)
{
    int count = 0;
    while (a) {
        if (a & 1)
            count += 1;
        a = a >> 1;
    }
    return count;
}

// custom comparator of std::sort
int cmp(int a, int b)
{
    int count1 = countBits(a);
    int count2 = countBits(b);

    // this takes care of the stability of
    // sorting algorithm too
    if (count1 <= count2)
        return false;
    return true;
}
class Solution{
    public:
    void sortBySetBitCount(int arr[], int n)
    {
        // Your code goes here
        stable_sort(arr,arr+n,cmp);
    }
};

// { Driver Code Starts.

int main()
{
    int t;
    cin>>t;
    while(t--){
        int n;
        cin>>n;
        int arr[n];
        for(int i=0;i<n;i++){
            cin>>arr[i];
        }
        Solution ob;
        ob.sortBySetBitCount(arr, n);
        for (int i = 0; i < n; i++)
            cout << arr[i] << " ";
        cout << endl;
    }
    return 0;
}
  // } Driver Code Ends