zoj 1938 Binomial Showdown 组合数裸基础

Binomial Showdown

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Time Limit: 2 Seconds      Memory Limit:65536 KB

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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。