#include <iostream>
#include <algorithm>
#include <cstring>
#include <unordered_map>
#include <set>

using namespace std;

int main()
{
    int t;
    cin >> t;
    while(t -- )
    {
        int n;
        string a;
        cin >> n >> a;

        set<char> u_str(a.begin(), a.end());

        string b = string(u_str.begin(), u_str.end());

        unordered_map<char, char> each_str;

        for(int i = 0; i < b.length(); i ++ )
        {
            each_str[b[i]] = b[b.length() -i - 1]; 
        }

        string s;
        for(auto t : a)
        {
            s += each_str[t];
        }

        cout << s << endl;
    }

    return 0;
}