集合的划分

#include<iostream>
#include<cstdio>
#include<cstdlib>
using namespace std;
int hf(int n,int k)
{
if(n<k||k==0)return 0;
if(n==k||k==1)return 1;
return hf(n-1,k)*k+hf(n-1,k-1);
}
void write(long long x)
{
if(!x)return;
write(x/10);
putchar(x%10+‘0‘);
}
int main()
{
int n,k;
scanf("%d%d",&n,&k);
write(hf(n,k));
return 0;
}