题解，但递归

#include<stdio.h>
#define ll long long //宏定义(ll==long long)
ll A(ll n,ll k){ //递归函数
    return k==0?1:(k==1?n:(n-k+1)*A(n,k-1));
    /*
     *如果k==0，直接返回1
     *如果k==1，直接返回n
     *否则返回(n-k+1)*A(n,k-1)
     */
}
signed main(int argc,char** argv){ //防伪
    ll n,k;
    scanf("%lld %lld",&n,&k);
    printf("%lld",A(n,k));
}