print all permutation of a list

jinzhou_7_perm.c

#include <stdio.h>
#include <malloc.h>
#include <string.h>

/* two solution:
 * 1. function "perm"
 * 2. function "print_permutation"
 */

void swap(int data[], int a, int b)
{
    int tmp = data[a];
    data[a] = data[b];
    data[b] = tmp;
}

/* [4 1 2 3] => [1 2 3 4] */
void rotate_one_left(int data[], int len)
{
    int tmp = data[0];
    memcpy(data, data+1, (len-1)*sizeof(*data));
    data[len-1] = tmp;
}

void print_data(int data[], int len)
{
    int i;
    for (i = 0; i < len; i++) {
        printf("%d", data[i]);
    }
    printf("\n");
}

/* this one use no additional space */
void perm(int data[], int len, int level)
{
    if (level >= len - 1) {
        print_data(data, len);
        return;
    }

    int i;
    for (i = level; i < len; i++) {
        swap(data, i, level);
        perm(data, len, level + 1);
    }

    rotate_one_left(data+level, len-level);
}

void print_permutation(int data[], int len, const char *prefix)
{
    if (len <= 0) {
        printf("%s\n", prefix);
        return;
    }

    int *sub_array= (int *)malloc(len * sizeof(*sub_array));
    memcpy(sub_array, data, len*sizeof(*sub_array));

    int i, j, k;
    char new_prefix[BUFSIZ];

    for (i = 0; i < len; i++) {
        sprintf(new_prefix, "%s%d", prefix, data[i]);

        swap(sub_array, i, 0);
        print_permutation(sub_array+1, len-1, new_prefix);
    }
}

int main(int argc, const char *argv[])
{
    int data[] = {1, 2, 3, 4, 5, 6, 7};
    /*print_permutation(data, 7, "");*/
    perm(data, 7, 0);
    return 0;
}