Jia Tse
www.egr.unlv.edu/~jjtse


/*
http://www.cs.utexas.edu/users/djimenez/utsa/cs3343/lecture25.html
*/

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

void combinations (int v[], int start, int n, int k, int maxk) {
  int     i;

  /* k here counts through positions in the maxk-element v.
   * if k > maxk, then the v is complete and we can use it.
   */
  if (k > maxk) {
    /* insert code here to use combinations as you please */
    for (i=1; i<=maxk; i++) printf ("%i ", v[i]);
    printf ("\n");
    return;
  }

  /* for this k'th element of the v, try all start..n
   * elements in that position
   */
  for (i=start; i<=n; i++) {

    v[k] = i;

    /* recursively generate combinations of integers
     * from i+1..n
     */
    combinations (v, i+1, n, k+1, maxk);
  }
}

int main (int argc, char *argv[]) {
  int     v[100], n, k;

  if (argc != 3) {
    printf ("Usage: %s n k\n", argv[0]);
    exit (1);
  }
  n = atoi (argv[1]);
  k = atoi (argv[2]);

  /* generate all combinations of n elements taken
   * k at a time, starting with combinations containing 1
   * in the first position.
   */
  combinations (v, 1, n, 1, k);
  exit (0);
}