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.
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.
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.
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，数据比较小，直接暴力枚举运算即可！
AC代码：
1 #include<iostream> 2 using namespace std; 3 int main(){ 4 int n,k;long long ans;//开long long，避免数据溢出 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 }