POJ1942-Paths On a Grid-组合数学

从n+m步中挑选min(n,m)步向上走，剩下的就是向下走。

求解n+mCmin(n,m)时，要一边计算一边约分。

 

#include <cstdio>
#include <algorithm>
#include <iostream>

using namespace std;
unsigned int n,m;

unsigned int Com(unsigned int m,unsigned int n)
{
    double cnm = 1.0;
    while(n > 0)
        cnm *= (double)(m--)/(double)(n--);
    cnm += 0.5;
    return (unsigned int)cnm;
}

int main()
{
    while(cin>>n>>m && (n||m) )
    {
        cout << Com(n+m,min(n,m))<<endl;
    }
}