rt，交了好几发了。

#include <iostream>
#include <set>
using namespace std;
long long a[1010];
int main()
{
    int t;
    cin >> t;
    while (t--) {
        set<int> s;
        int n;
        cin >> n;
        for (int i = 1; i <= n; i++) cin >> a[i];
        for (long long k = 2; ; k *= 2) {
            s.clear();
            for (int i = 1; i <= n; i++)
                s.insert(a[i] % k);
            if (s.size() == 2) {
                cout << k << endl;
                break;
            }
        }
    }
    return 0;
}