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]); } }