D - Dance (Atcoder)

#include <bits/stdc++.h>

using namespace std;

const int N = 17;

int n, ans = 0;
int A[N][N], used[N];

void rec(int couples, int xr) {
    if (couples == n) {
        ans = max(ans, xr);
        return;
    }

    int i = 1;
    while (used[i]) i++;

    for (int j = i + 1; j <= 2 * n; j++) {
        if (used[j] == 0) {
            used[i] = used[j] = 1;
            rec(couples + 1, xr ^ A[i][j]);
            used[i] = used[j] = 0;
        }
    }
}

int main(){
    cin >> n;

    for (int i = 1; i <= 2 * n; i++) {
        for (int j = i + 1; j <= 2 * n; j++) {
            cin >> A[i][j];
        }
    }

    rec(0, 0);

    cout << ans << endl;
}