JavaCode

import java.io.*;
import java.util.*;

public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int Q = sc.nextInt();
        while(Q-- > 0){
            int n = sc.nextInt();
            String[] numbers = new String[n];
            for(int i=0; i<n; i++) numbers[i] = sc.next();
            Arrays.sort(numbers, new Comparator<String>(){
                @Override
                public int compare(String s1, String s2){
                    return (s2 + s1).compareTo(s1 + s2);
                }
            });

            for(String el: numbers){
                System.out.print(el);
            }
            System.out.println();
        }
    }
}