Largest number formed from array

#include<iostream>
#include<cstdio>
#include<algorithm>
#include<vector>
using namespace std;
void show_vector(vector<string> s){
    for(auto i = s.begin(); i < s.end(); i++){
        cout << *i;
    }
    cout << endl;
}

bool comp(string s1, string s2){
    string s1s2 = s1+s2;
    string s2s1 = s2+s1;
    return (s1s2>s2s1);
}

int main(){
    int t; scanf("%d", &t);
    while(t--){
        int n; scanf("%d", &n);
        vector<string> a;
        for(int i = 0; i < n; i++){
            string s; cin >> s;
            a.push_back(s);
        }
        //show_vector(a);
        sort(a.begin(), a.end(), comp);
        show_vector(a);
    }
}