用a-z,0-9组合成所有可能的三位密码

#include<stdio.h>
#include<stdlib.h>
#include<assert.h>

void combination_cursion(int *a, int len, int m, int *out, int out_len) {
int i;
if (m == 0)//out中已经存储了m个数字
{
for (i = 0; i < out_len; i++)
printf("%d\t", out[i]);
printf("\n");
return;
}

for (i = len; i >= m; i--)//从前向后依次选定一个，动态规划的体现
{
out[m - 1] = a[i - 1];//选定一个之后
combination_cursion(a, i - 1, m - 1, out, out_len);//从前i-1个后选m-1，递归
}
}

void print_combination_cursion(int *a, int n, int m) {
assert(a != NULL);
assert(n >= m);
int *out = (int *) malloc(sizeof(int) * m);
combination_cursion(a, n, m, out, m);
}

int main() {
int array[] = {1, 2, 3, 4, 5};
print_combination_cursion(array, sizeof(array) / sizeof(int), 3);
return 0;
}