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; }