1974b

//Author :- Tushar 
//Date:- 2024-05-20 21:15:03
#include <bits/stdc++.h>
using namespace std;
#define int long long
#define letsgooooooooooo            \
  ios_base::sync_with_stdio(false); \
  cin.tie(NULL);                    \
  cout.tie(NULL);
#define test         \
  int Tushars_07;    \
  cin >> Tushars_07; \
  while (Tushars_07--)
#define endl "\n"
#define no cout<<"NO \n";
#define yes cout<<"YES \n";
// const ll mod = 1000000007;
// const ll mod = 998244353;


int32_t main() {
  letsgooooooooooo cout << fixed << setprecision(7);
  test{
    int n; cin >>n ; 
    string str ; cin >> str ; 
    set<char> s ; 
    for(int i = 0 ; i < n ; i++){
      s.insert(str[i]);
    }
    string ans ; 
    for(auto i : s){
      ans += i ; 
    }
    string out ; 
    for(int i = 0 ; i<str.size() ; i++){
      out.push_back()
    }
  }


  return 0;
}