ACM刷题之HDU————N！Again

N！Again

Time Limit: 2000/1000 MS (Java/Others) Memory Limit: 32768/32768 K (Java/Others)Total Submission(s): 1152 Accepted Submission(s): 644 

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

24120

 

看着吓人，其实纸老虎

下面是ac代码

#include<stdio.h>#include<stdlib.h>#include<string.h>#include<math.h>int main(){__int64 a=1,i,j,y=0,flags=1,shi,ge,len;int b[10000];char x[10000];char c,t;while(scanf("%s",x)!=EOF){a=1;len=strlen(x);if(len>2)printf("0\n");else{if(len==2){ge=x[1]-'0';shi=x[0]-'0';shi=shi*10;i=shi+ge;}elsei=x[0]-'0';for(j=1;j<=i;j++){a*=j;a=a%2009;}printf("%I64d\n",a); }}} 

41的阶乘%2009 已经等于0了，再增大也还是会等于0.

所以分开判断就好了。。

至于为什么41的阶乘%2009为0，我是怎么发现的，建议可以边阶乘边对2009取余，并输出。你会发现第41个的输出为0，而且之后的都为0。