hdu 2049 考新郎

#include <stdio.h>__int64 com(int n,int m) {    int i;    __int64 top = 1,bottom  = 1;    for(i = 1;i <= m;i ++){        bottom = bottom * i;    }    for(i = n;i > n-m;i--) {        top = top * i;    }    return top/bottom;}int main() {    int m,n,sum,i;    __int64 a[21];    a[1] = 0;    a[2] = 1;    for(i = 3;i <= 20;i ++) {        a[i] = (a[i-1] + a[i-2]) * (i-1);    }    scanf("%d",&sum);    while(sum--) {        scanf("%d %d",&n,&m);        printf("%I64d\n",com(n,m)*a[m]);    }}