View Code of Problem 3929

#include<iostream>
#include<vector>
#include<unordered_map>
using namespace std;
int main()
{
	int t;
	scanf("%d",&t);
	while(t --)
	{
		int n;
		scanf("%d",&n);
		unordered_map<long,int> res;
		for(int i = 0;i < n;i ++) 
		{
			long a;
			cin >> a;
			res[a] ++;
		}
		long ans = 0;
		for(auto x : res)
		{
			if(x.second%2==1) ans ^= x.first;
		}
		cout << ans << endl;
	}
	return 0;
}