// Sort of non-deterministic

#include <iostream>
#include <cstring>

using namespace std;

void print(int board[], int size)
{ for (int r = 0; r < size; r += 1)
  { for (int c = 0; c < size; c += 1)
      if (board[r] == c)
        cout << "X";
      else
        cout << "-";
    cout << "\n"; }
  cout << "\n"; }

void put_queens(int board[], int size)
{ bool * col_used = new bool[size];
  bool * plus_diag_used = new bool[2 * size - 1];
  bool * minus_diag_used = new bool[2 * size - 1];

  while (true)
  { memset(col_used, 0, size * sizeof(bool));
    memset(plus_diag_used, 0, (2 * size - 1) * sizeof(bool));
    memset(minus_diag_used, 0, (2 * size - 1) * sizeof(bool));
    for (int r = 0; r < size; r += 1)
    { cout << "row " << r << "\n";
      while (true)
      { int c = random() % size;
        cout << "  r = " << r << ", c = " << c << ": ";
        if (col_used[c])
        { cout << "reject, column used\n";
          continue; }
        if (plus_diag_used[r + c])
        { cout << "reject, plus diagonal used\n";
          continue; }
        if (minus_diag_used[r - c + size - 1])
        { cout << "reject, minus diagonal used\n";
          continue; }
        cout << "accept\n";
        board[r] = c;
        col_used[c] = true;
        plus_diag_used[r + c] = true;
        minus_diag_used[r - c + size - 1] = true;
        break; } }
    print(board, size);
    return; } }

int main(int argc, char * argv[])
{ int size = 8;
  if (argc > 1)
  { char * c;
    size = strtol(argv[1], & c, 10);
    if (* c != '\0' || size < 1)
    { cerr << argv[1] << " is not a usable number\n";
      exit(1); } }
  srandomdev();

  int * board = new int[size];
  put_queens(board, size);
  delete [] board; }