POJ 2249 Binomial Showdown 求组合数C(n,k)

http://poj.org/problem?id=2249

Binomial Showdown

Time Limit:1000MS

Memory Limit:65536K

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

4 2
10 5
49 6
0 0

Sample Output

6
252
13983816

/* Author : yan
 * Question : POJ 2249 Binomial Showdown
 * Date && Time : Thursday, February 03 2011 06:05 PM
 * Compiler : gcc (Ubuntu 4.4.3-4ubuntu5) 4.4.3
*/
#include<stdio.h>
double comb(int n,int k)
{
	double ans = 1;
	int i;
	for(i=1;i<=k;i++)
	{
		ans*=(double)(n-i+1)/(double)i;
	}
	return ans;
}
int main()
{
	freopen("input","r",stdin);
	int n,m;
	while(scanf("%d %d",&n,&m) && n)
	{
		m=m<(n-m)?m:(n-m);
		printf("%.0f/n",comb(n,m));
	}
	return 0;
}