CppCode

#include <bits/stdc++.h>
using namespace std;

int main() {
    /* Enter your code here. Read input from STDIN. Print output to STDOUT */
    int Q;
    cin >> Q;
    while(Q--){
        int n;
        cin >> n;
        vector<string> input(n);
        for(int i=0; i<n; i++) cin >> input[i];
        auto lambda = [](string a, string b){
            return a + b > b + a;
        };
        sort(input.begin(), input.end(), lambda);
        string ans = "";
        for(auto el : input) ans += el;
        cout << ans << endl;
    }
    return 0;
}