LightOJ-1005 组合数学，组合数水题

#include<bits/stdc++.h>
using namespace std;
#pragma comment(linker, "/STACK:102400000,102400000")
#define F(i,a,b)  for (int i=a;i<b;i++)
#define FF(i,a,b) for (int i=a;i<=b;i++)
#define mes(a,b)  memset(a,b,sizeof(a))
#define INF 0x3f3f3f3f
typedef long long ll;
const int N = 1e5+10;

double C(double n, double m)
{
    double sum_n = 1, sum_m = 1;
    for(double i=n; i>=n-m+1; i--)
        sum_n *= i;
    for(double i=m; i>=1; i--)
        sum_m *=i;
    return sum_n/sum_m;
}
double A(double n, double m)
{
    double sum_n = 1;
    for(double i=n; i>=n-m+1; i--)
        sum_n *= i;
    return sum_n;
}
int main()
{
    int T;
    double n, k;
    cin>>T;
    FF(cas,1,T) {
        cin>>n>>k;
        printf("Case %d: %.0f\n", cas, C(n, k)*A(n, k));
    }

    return 0;
}