View Code of Problem 3929

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

int a[10];
int main()
{
    int n;
    cin >> n;
    while (n--)
    {
        int m;
        cin >> m;
        for (int i = 0; i < m; i++)
        {
            int x;
            cin >> x;
            a[x]++;
        }
        int s[10] = { 0 };
        for (int i = 0; i <= 9; i++)
        {
            if (a[i]%2!=0)
            {
                s[i]=1;
            }
        }
        int b;
        for (int i = 0; i < 10; i++)
        {
            if (s[i])
            {
                b = i;
                s[i] = 0;
                break;
            }
        }
        for (int i = 0; i < 10; i++)
        {
            if (s[i])
            {
                b ^= i;
            }
        }
        cout << b << endl;

    }
}