Alone in couple

#include<iostream>
#include<cstdio>
using namespace std;

int main(){
    int t; scanf("%d", &t);
    while(t--){
        int n; scanf("%d", &n);
        int a = 0, i;
        for(i = 0; i < n; i++){
            int k; scanf("%d", &k);
            a ^= k;
        }
        cout << a << endl;
    }
}