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.
Sample Input
4 2
10 5
49 6
0 0
Sample Output
6
252
13983816
之前遇到的组合数都稍微复杂一点，所以习惯用唯一分解来解决。这道题就是纠结了一下，还是懒得写唯一分解了，麻烦。
#include<cstdio>
#include<cstdlib>
#include<iostream>
#include<math.h>
#include<algorithm>
using namespace std;
int main()
{
long long n,m;
long long ans;
while(cin>>n>>m)
{
if(n==0) return 0;
if(n-m<m) m=n-m;
ans=1;
for(int i=1;i<=m;i++)
ans=ans*(n-i+1)/i;//不过先乘后除会不会超出longlong呢？？？
cout<<ans<<endl;
}
return 0;
}假如先乘法感觉有数据会超吧，怎么处理呢？？？求大神指教。