@*Intro. This program makes {\mc DLX} data to find all ways to attack
or occupy
all cells of an $n\times n$ board with $m$ queens.

@d maxn 16 /* hexadecimal limitation */

@c
#include <stdio.h>
#include <stdlib.h>
int m,n; /* command-line parameters */
main(int argc,char*argv[]) {
  register int i,j,k;
  @<Process the command line@>;
  @<Print the item-name line@>;
  for (i=0;i<n;i++) for (j=0;j<n;j++)
    @<Print the option for a queen at position $(i,j)$@>;
}

@ @<Process the command line@>=
if (argc!=3 || sscanf(argv[1],"%d",
                      &n)!=1 ||
               sscanf(argv[2],"%d",
                      &m)!=1) {
  fprintf(stderr,"Usage: %s n m\n",
                 argv[0]);
  exit(-1);
}
if (n>maxn) {
  fprintf(stderr,"Sorry, I don't presently allow n>%d!\n",
                           maxn);
  exit(-2);
}
printf("| %s %d %d\n",
               argv[0],n,m);

@ @<Print the item-name line@>=
for (i=0;i<n;i++) for (j=0;j<n;j++)
  printf("1:%d|%x%x ",
                m,i,j);
printf("%d|Q\n",
                m);

@ @<Print the option for a queen at position $(i,j)$@>=
{
  printf("Q %x%x",
           i,j);
  for (k=0;k<n;k++) if (k!=i)
    printf(" %x%x",
             k,j);
  for (k=0;k<n;k++) if (k!=j)
    printf(" %x%x",
             i,k);
  for (k=1;i+k<n && j+k<n;k++)
    printf(" %x%x",
              i+k,j+k);
  for (k=1;i-k>=0 && j-k>=0;k++)
    printf(" %x%x",
              i-k,j-k);
  for (k=1;i+k<n && j-k>=0;k++)
    printf(" %x%x",
              i+k,j-k);
  for (k=1;i-k>=0 && j+k<n;k++)
    printf(" %x%x",
              i-k,j+k);
  printf("\n");
}

@*Index.