func_code_string: #include <bits/stdc++.h>   using namespace std;   const int M = 1e9 + 7;   int main() {     ios_base::sync_with_stdio(false);     cin.tie(NULL);     int t;     cin >> t;     while (t--) {       int n;       cin >> n;       int a[n + 1];       for (int i = 0; i < n; i++) cin >> a[i];       map<int, int> mp;       if (n & 1) {         cout << -1 << endl;         continue;       }       for (int i = 0; i < n; i++)         for (int j = i + 1; j < n; j++) mp[a[i] ^ a[j]]++;       int ans = -1;       for (auto it = mp.begin(); it != mp.end(); it++) {         if (it->second == (n / 2)) {           ans = it->first;           break;         }       }       cout << ans << endl;     }   }   