poj 2249 Binomial Showdown

Binomial Showdown

Time Limit: 1000MS		Memory Limit: 65536K
Total Submissions: 14828		Accepted: 4549

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 231.
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

#include<iostream>
using namespace std;

__int64 fun(int a , int b , int c)
{
__int64 kk = 1 ;
int wk = a , wk2 = 1 ;
for(wk = c ; wk >= b + 1 ; wk-- )
{
kk *= wk ;
if( kk % a == 0 && a > 0)
kk /= a-- ;
}
while( a && a >= 1 )
{
wk2 *= a-- ;
}
return kk / wk2;
}

int main()
{
int N = 0 , M = 0 ;
while( scanf( "%d%d" , &N , &M) , N + M !=0)
{
int min = 0, max =0 ;
if( N - M > M )
{
min = M ;
max = N - M ;
}
else
{
max = M;
min = N - M ;
}
cout<<fun( min , max , N)<<"\n" ;
}
return 0;
}