CUC-SUMMER-3-N

N - N!

HDU - 1042

Given an integer N(0 ≤ N ≤ 10000), your task is to calculate N!

Input
One N in one line, process to the end of file.

Output
For each N, output N! in one line.

Sample Input
1
2
3
Sample Output
1
2
6

题意：求n的阶乘

解法：n最大10000一定超出longlong，高精度计算，数组每一项存4位数，使得与n相乘最大为10^9在int范围内

代码：

#include<iostream>
#include<cstring>
using namespace std;
#define maxn 50000
int x[maxn];
int main()
{
    int a;
    while(cin>>a){
        if(a==0){
            cout<<"1"<<endl;
            continue;
        }
        memset(x, 0, sizeof(x));
        x[0]=1;
        for(int i=2;i<=a;i++){
            int temp=0;
            for(int j=0;j<maxn;j++){
                x[j]=x[j]*i+temp;
                temp=x[j]/10000;
                x[j]%=10000;
            }
        }
        int flag=0;
        for(int i=maxn;i>=0;i--){
            if(flag==1)
                printf("%04d",x[i]);
            else
                if(x[i]!=0){
                    cout<<x[i];
                    flag=1;
                }
        }
        cout<<endl;
    }

}