/* Generates all possible placements of n non-attacking queens on an nxn board. */

#include <stdio.h>
#include <stdlib.h>

#define MAX 12

int n;

int A[MAX];
int sol[MAX];
int B[2*MAX-1];
int C[2*MAX-1];

void PrintIt(void) {
  int i;

  for (i=0; i < n ; i ++)  printf(" %2d", sol[i] + 1);

  printf("\n");
}

void Q(int col) {
  int row;

  for (row=0; row < n; row ++) {
    if (A[row] && B[row + col] && C[row - col + (n-1)]) {
	sol[col] = row;
	A[row] = 0;
	B[row + col] = 0;
	C[row - col +(n-1)] = 0;
	if (col < n-1)
	  Q(col+1);
	else
	  PrintIt();
	A[row] = 1;
	B[row + col] = 1;
	C[row - col + (n-1)] = 1;
      }
  }
}

int main(int argc, char *argv[]) {
  int i;

  if (argc != 2) {
    printf("\n A single argument expected.\n");
    return 1;
  }

  n = atoi(argv[1]);


  if (n < 0) {
    printf("\n Positive number expected.\n");
    return 2;
  }

  if (n > MAX) {
    printf("\n Number not greater than %d expected.\n", MAX);
    return 3;
  }


  for (i=0; i < n; i ++) A[i] = 1;

  for (i=0; i < 2*n-1; i ++) {B[i] = 1; C[i] = 1;}
  
  Q(0);

  return 0;
}