最小字符串

#include <bits/stdc++.h>
using namespace std;
bool cmp(string const s1, string const s2) {
    return s1 + s2 < s2 + s1;
}
int main() {
    ios::sync_with_stdio(false);
    int t;
    cin >> t;
    while (t--) {
        vector<string> vec;
        int n;
        cin >> n;
        while (n--) {
            string temp;
            cin >> temp;
            vec.push_back(temp);
        }
        sort(vec.begin(), vec.end(), cmp);
        for (vector<string>::iterator it = vec.begin(); it != vec.end(); it++) {
            cout << *it;
        }
        cout << endl;
    }
    return 0;
}