lightoj 1005 组合数学

题目链接：http://lightoj.com/volume_showproblem.php?problem=1005

#include <cstdio>
#include <cstring>
#include <iostream>
#include <cmath>
#include <algorithm>
#include <queue>
#include <vector>
using namespace std;

const int maxe = ;
const int maxn = ;
const int INF  = 0x3f3f3f;

float dp[maxn];
long long C[maxn][maxn];
long long A[maxn][maxn];

int main()
{
    //freopen("E:\\acm\\input.txt","r",stdin);
    int T;
    cin>>T;
    for(int i=;i<=;i++)  C[i][] = ;
    A[][] = ;
    for(int i=;i<=;i++)  A[i][i] = A[i-][i-]*i;
    for(int n=;n<=;n++)
        for(int k=;k<=n;k++){
            C[n][k] = C[n][k-] * (n-k+)/k;
            A[n][k] = C[n][k]*A[k][k];
        }

    for(int t=;t<=T;t++){
        int n,k;
        cin>>n>>k;
        printf("Case %d: ",t);
        dp[] = ;
        if(k > n )     printf("0\n");
        else if(k ==  ) printf("1\n");
        else{
            cout<<A[n][k]*C[n][k]<<endl;
        }
    }
}