HDU2519组合数快速算法

                        #define DeBUG
#include <iostream>
#include <cstdio>
#include <cstring>
#include <cmath>
#include <cstdlib>
#include <algorithm>
#include <vector>
#include <stack>
#include <queue>
#include <string>
#include <set>
#include <sstream>
#include <map>
#include <bitset>
using namespace std ;
#define zero {0}
#define INF 2000000000
#define EPS 1e-6
typedef long long LL;
const double PI = acos(-1.0);
inline int sgn(double x){return fabs(x) < EPS ? 0 :(x < 0 ? -1 : 1);}
unsigned __int64 N(unsigned __int64 n)
{
    if(n==0)
        return 1;
    return N(n-1)*n;
}
double C(int n,int m)
{
    if(m>n)
        return 0;
    if(m<n/2.0)
        m=n-m;
    double s1=0;
    for(int i=m+1;i<=n;i++)
    {
        s1+=log((double)i);
    }
    double s2=0;
    int ub=n-m;
    for(int i=2;i<=ub;i++)
    {
        s2+=log((double)i);
    }
    if(m>n)
        return 0;
    return exp(s1-s2);
}
int main()
{    
    #ifdef DeBUGs
        freopen("C:\\Users\\Sky\\Desktop\\1.in","r",stdin);
    #endif
        int T;
        scanf("%d", &T);
        while(T--)
        {
            unsigned __int64 n,m;
            cin>>n>>m;
            if(m>n)
                printf("0\n");
            else
            printf("%.0lf\n", C(n,m));
        }
    
    return 0;
}