hdu 2674 N！Again 数论水题啊~~~

N！Again

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 3803    Accepted Submission(s): 2036

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
   
   
   
   

 这题最容易想到的是2009以后全是0。。。至少我第一次A的代码就是这个思路。2009以前的打表~~

其次，2009=41*7*7。所以40以后全都是0了。至于40以前的也是打表呗~

附上我的代码：

#include <stdio.h>
#define MAX 2009

int ans[MAX] ;

int main()
{
	int n ;
	ans[0] = 1 ;
	for(int i = 1 ; i < MAX ; ++i )
	{
		ans[i] = (ans[i-1]*i)%MAX ;
	}
	while(~scanf("%d",&n))
	{
		if(n>=2009)
		{
			puts("0") ;
		}
		else
		{
			printf("%d\n",ans[n]) ;
		}
	}
	return 0;
}

与君共勉