链接：click here
题意：
In how many ways can you choose k elements out of n elements, not taking order into account? Write a program to compute this number.
给你整数n和k，让你求组合数c(n,k)。
代码：
#include <cstdio>
#include <cstring>
#include <math.h>
typedef long long LL;
LL ans,n,k;
int main()
{
while(scanf("%lld%lld",&n,&k),n)
{
ans=1;
if(k == 0)
{
printf("1\n");
continue;
}
k=n-k>k?k:n-k;
//if(k>n-k)k=n-k;
for(int i=1; i<=k; i++)
{
ans=ans*(n-i+1)/i;
}
printf("%lld\n",ans);
}
return 0;
}
ZOJ 1938 Binomial &&poj 2249 （Binomial Showdown ）（睡前一水）
原文：http://blog.csdn.net/u013050857/article/details/43126031