#include "cs.h"
/* return a random permutation vector, the identity perm, or p = n-1:-1:0.
 * seed = -1 means p = n-1:-1:0.  seed = 0 means p = identity.  otherwise
 * p = random permutation.  */
int *cs_randperm (int n, int seed)
{
    int *p, k, j, t ;
    if (seed == 0) return (NULL) ;	/* return p = NULL (identity) */
    p = cs_malloc (n, sizeof (int)) ;	/* allocate result */
    if (!p) return (NULL) ;		/* out of memory */
    for (k = 0 ; k < n ; k++) p [k] = n-k-1 ;
    if (seed == -1) return (p) ;	/* return reverse permutation */
    srand (seed) ;			/* get new random number seed */
    for (k = 0 ; k < n ; k++)
    {
	j = k + (rand ( ) % (n-k)) ;    /* j = rand int in range k to n-1 */
	t = p [j] ;			/* swap p[k] and p[j] */
	p [j] = p [k] ;
	p [k] = t ;
    }
    return (p) ;
}
