全排列--递归

#include <stdio.h>

#define MAX 4
void perm(int *, int, int);

void main()
{
    int array[MAX] = {1,2,2,3};

    perm(array,0,MAX-1);
}

void perm(int *p, int k, int m)
{
    int i;
    int tmp;

    if(k == m) {
        for(i = 0; i <= m; i++)
            printf("%d ", p[i]);
        printf("\n");
    }
    else {
        for(i = k; i <= m; i++) {
            int j,mark = 0;

            for(j = k; j < i; j++) {
                if(p[j] == p[i]) {mark = 1;break;}
            }
            if(!mark) {
                tmp = p[i];
                p[i] = p[k];
                p[k] = tmp;

                perm(p,k+1,m);

                tmp = p[i];
                p[i] = p[k];
                p[k] = tmp;
            }
        }
    }
}

复杂度：T(N)=N*T(N-1)+c(N). T(N)=O(N!)