POJ 1942 Paths on a Grid

代码：

#include<iostream>

using namespace std;

long long comb(long long m, long long n)
{
    long long s=1;
    m=n-m>m?m:n-m;
    long long k=1, i;
    for (i=0; i<m; i++)
    {
        s*=n-i;
        while(k <=m && s%k==0)
        {
            s/=k;
            k++;
        }
    }
    return s;
}

int main()
{
    long long a, b;
    while(cin >> a >> b, a || b)
    {
        cout << comb(a, a+b) << endl;
    }
    return 0;
}