POJ 题目2249 Binomial Showdown（数学）

最新推荐文章于 2018-09-02 08:49:54 发布

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本文详细介绍了如何解决组合数学中的二项式系数计算问题，包括输入格式、输出要求及样例输入输出解析。

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Binomial Showdown

Time Limit: 1000MS		Memory Limit: 65536K
Total Submissions: 18358		Accepted: 5600

Description

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.

Input

The input will contain one or more test cases.
Each test case consists of one line containing two integers n (n>=1) and k (0<=k<=n).
Input is terminated by two zeroes for n and k.

Output

For each test case, print one line containing the required number. This number will always fit into an integer, i.e. it will be less than 2 ³¹.
Warning: Don't underestimate the problem. The result will fit into an integer - but if all intermediate results arising during the computation will also fit into an integer depends on your algorithm. The test cases will go to the limit.

Sample Input

Sample Output

6
252
13983816

Source

Ulm Local 1997

ac代码

#include<stdio.h>
#include<string.h>
__int64 c(int a,int b)
{
	__int64 ans=1;
	int i;
	if(b>a/2)
		b=a-b;
	for(i=1;i<=b;i++)
	{
		ans*=(a-i+1);
		ans/=i;
	}
	return ans;
}
int main()
{
	int a,b;
	while(scanf("%d%d",&a,&b)!=EOF,a||b)
	{
		printf("%I64d\n",c(a,b));
	}
}