public int eightQueens(int column) {
  if (column == N) {
    return 1;
  }
  int counter = 0;
  for (int row = 0; row < N; row++) {
    if (rows[row] || diagonal45[column + row] || diagonal135[row-column+N-1]) continue;
    rows[row] = true;
    diagonal45[row + column] = true;
    diagonal135[row-column+N-1] = true;
    counter += eightQueen(column + 1);
    rows[row] = false;
    diagonal45[row + column] = false;
    diagonal135[row-column+N-1] = false;
  }
  return counter;
}