HDU 2674 N！Again （数论）

N！Again

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 4606    Accepted Submission(s): 2415

Problem Description

WhereIsHeroFrom:             Zty, what are you doing ?
Zty:                                     I want to calculate N!......
WhereIsHeroFrom:             So easy! How big N is ?
Zty:                                    1 <=N <=1000000000000000000000000000000000000000000000…
WhereIsHeroFrom:             Oh! You must be crazy! Are you Fa Shao?
Zty:                                     No. I haven's finished my saying. I just said I want to calculate N! mod 2009


Hint : 0! = 1, N! = N*(N-1)!

 

Input

Each line will contain one integer N(0 <= N<=10^9). Process to end of file.

 

Output

For each case, output N! mod 2009

 

Sample Input

   
   
   
   

    
    
    
    4 
5
   
   
   
   

 

Sample Output

   
   
   
   

    
    
    
    24
120
   
   
   
   

 

  本人目前太菜，刚接触到真正的数论，为什么要说是真正的呢？因为以前曾经见过不少这种题目，一直以为是不涉及算法的题目，只是因为我不认识它而已。

  这个题目需要打表，把前2009个阶乘打表出来，因为2009后面是2008！*2009*……，所以后面的一定是0.

#include<iostream>
#include<cstdio>
using namespace std;
int main()
{
    int n,a[2009]={1};
    for(int i=1;i<=2009;i++)//打表
    {
        a[i]=a[i-1]*i;
        a[i]%=2009;
    }
    while(~scanf("%d",&n))
    {
        if(n<2009)
            printf("%d\n",a[n]);
        else//后面都是0
        printf("0\n");
    }
    return 0;
}