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
解题思路：简单求组合数，水过！
AC代码：
1 #include<iostream>
2 using namespace std;
3 int main(){
4 int n,k;long long ans;
5 while(cin>>n>>k&&(n+k)){
6 if(n-k<k)k=n-k;
7 ans=1;
8 for(int i=1;i<=k;++i)ans=ans*(n-i+1)/i;
9 cout<<ans<<endl;
10 }
11 return 0;
12 }
N - Binomial Showdown （组合数学）
原文：https://www.cnblogs.com/acgoto/p/9315865.html
