hdu 2519 新生晚会

#include<stdio.h>int main(){__int64 sum;int t;int i;int n,m;scanf("%d",&t);while(t--){scanf("%d%d",&n,&m);if(m>n){printf("0\n");continue;}sum=1;for(i=1;i<=m;i++){sum=sum*(n-i+1)/i;}printf("%I64d\n",sum);}return 0;}