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)!
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
最容易想到的就是2009以后的阶乘都包含有2009这个因子,所以对2009取模都是0,结论,10的9次方纯属吓唬人的!再深入点,其实2009=41x7x7 也就是到40以后都是0了!
代码如下:
#include<stdio.h> int main() { int n,sum,i,a[41]; a[0]=a[1]=1;sum=1; for(i=2;i<=40;i++) { sum*=i; sum%=2009; a[i]=sum; } while(scanf("%d",&n)!=EOF) { if(n<=40) printf("%d ",a[n]); else printf("0 "); } return 0; }