/* Article 19637 (318 more) in rec.games.chess:
From: jmurphy@athens.Princeton.EDU (Jerald Murphy)

Subject: Eight Queens problem
Message-ID: <1993Apr16.202749.11830@Princeton.EDU>
Originator: news@nimaster
Sender: jmurphy@athens (Jerald Murphy)
Nntp-Posting-Host: athens.princeton.edu
Organization: Princeton University
Date: Fri, 16 Apr 1993 20:27:49 GMT
Lines: 144


Here it is in c:

 Modified to do boards of different sizes and display files
 by Warren Porter  */

int *up, *down, *rank, *x;

unsigned int max=8, max2=16, max_less_1=7;

long int count=0;

print()
{
   int k;

   for (k = 0; k < max; k++) {
      printf(" %c%d", k + 97,x[k] + 1);
      }
   printf("\n");
   count++;
}

queens(int c)
{
   int r;

   for (r = 0; r < max; r++)
      if (rank[r] == 0 && up[r-c+max_less_1] == 0 && down[r+c] == 0) {
         rank[r] = 1;
         up[r-c+max_less_1] = 1;
         down[r+c] = 1;
         x[c] = r;
         if (c == max_less_1)
            print();
         else
            queens(c + 1);
         rank[r] = 0;
         up[r-c+max_less_1] = 0;
         down[r+c] = 0;
         }
}

main(int argc,char *argv[])
{
   int i;
   if (argc > 1)
      max=atoi(argv[1]),max2=max*2,max_less_1=max - 1;

   up=(int *)calloc(max2,sizeof(int));
   down=(int *)calloc(max2,sizeof(int));
   rank=(int *)calloc(max,sizeof(int));
   x=(int *)calloc(max,sizeof(int));
   for (i = 0; i < max2; i++)
      up[i] = down[i] = 0;
   for (i = 0; i < max; i++)
      rank[i] = x[i] = 0;
   queens(0);
   printf("\n There were %ld solutions for %d * %d\n",count,max,max);
}