N-Queens problem

#include "bits/stdc++.h"
using namespace std;
#define int unsigned long long
const int N = 50;

int MD, OD;
int row, col;
int cnt = 0, n;

inline bool val(int r, int c) {
  if (MD & (1LL<<(r+c))) return 0;
  if (OD & (1LL<<(r-c+n-1))) return 0;
  if (row & (1LL<<r)) return 0;
  if (col & (1LL<<c)) return 0;
  return 1;
}

inline void Set(int r, int c) {
  row |= (1LL<<r);
  col |= (1LL<<c);
  MD |= (1LL<<(r+c));
  OD |= (1LL<<(r-c+n-1));
}

inline void reset(int r, int c) {
  row -= (1LL<<r);
  col -= (1LL<<c);
  MD -= (1LL<<(r+c));
  OD -= (1LL<<(r-c+n-1));
}

int ans = 0;

void go(int curCol) {
  ++cnt;
  if (curCol == n) {
    cout << "Found\n";
    ++ans;
    exit(0);
    return;
  }
  for (int r = 0; r < n; ++r) {
    if (val(r, curCol)) {
      Set(r, curCol);
      go(curCol+1);
      reset(r, curCol);
    }
  }
}

signed main() {
  n = 30;
  cin >> n;
  go(0);
  cout << ans;
}