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#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) ;
}
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