(组合数学3.1.2.1)POJ 2249 Binomial Showdown(排列组合公式的实现)

/* * POJ_2249.cpp * *  Created on: 2013年10月8日 *      Author: Administrator */#include <iostream>#include <cstdio>using namespace std;typedef long long int64;int64 work(int64 n , int64 k){if(k > n/2){k = n-k;}int64 a = 1;int64 b = 1;int i;for(i = 1 ; i <= k ; ++i){a *= n-i+1;b *= i;if(a%b == 0){a /= b;b = 1;}}return a/b;}int main(){int64 n,k;while(scanf("%lld%lld",&n,&k)!=EOF,n){printf("%lld\n",work(n,k));}return 0;}