递归算法之全排列算法

算法描述：
R = {r1, r2, ..., rn}是要进行排列的n个元素，Ri = R-{ri}.
n == 1: perm(R) = (r),其中r是集合R中的唯一元素；
n > 1 : perm(R)由(r1)perm(R1),(r2)perm(R2),...,(rn)perm(Rn)构成。

代码：

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

#define MAX 100
int len, sum;
static int perm(char list[], int k, int m);
static int swap(char list[], int i, int j);

int main(int argc, char **argv)
{
        char list[MAX];

        fgets(list, sizeof(list), stdin);
        len = strlen(list);
        printf("Print result:\n");
        sum = perm(list, 0, len-2);//not include '\n'

        printf("sum = %d\n", sum);

        return(0);
}

static int perm(char list[], int k, int m)
{
        int i;

        if(k == len-2){
                for(i = 0; i<= m; i++){
                        printf("%c", list[i]);
                }
                sum++;
                printf("\n");
        }
        for(i = k; i <= m; i++){
                swap(list, k, i);
                perm(list, k+1, m);
                swap(list, k, i);
        }

        return sum;
}

static int swap(char list[], int i, int j)
{
        char temp;

        temp = list[i];
        list[i] = list[j];
        list[j] = temp;

        return 0;
}


[xxxx@localhost sousuo]$ ./a.out
123
Print result:
123
132
213
231
321
312
sum = 6