[Blue Bridge Cup][Basic Practice VIP] Factorial Calculation

Time Limit: 1Sec Memory Limit: 128MB Commits: 102 Resolved: 56

Topic description

Input a positive integer n, output the value of n!. 

where n!=1*2*3*…*n. 

The algorithm description 

n! may be very large, and the range of integers that the computer can represent is limited, which requires the use of high-precision computing methods. Use an array A to represent a large integer a, A[0] represents the ones digit of a, A[1] represents the tens digit of a, and so on. 

Multiplying a by an integer k becomes multiplying each element of array A by k, taking care to handle the corresponding carry. 

First set a to 1, then multiply by 2, multiply by 3, and when it is multiplied to n, the value of n! is obtained. 

enter

The input contains a positive integer n, where n<=1000. 

output

Output the exact value of n!.

sample input

10

Sample output

3628800

#include<iostream>
using namespace std;
const int maxn = 1000000;
long long n,a[maxn],len=1;
int main(void)
{
    cin>>n;
    a[0]=1;
    for(int i=2;i<=n;i++)
    {
        long long g=0;
        for(int j=0;j<len;j++) a[j]*=i;
        for(int j=0;j<len;j++)
        {
            //cout<<"g="<<g<<endl;
            /*
            a[j]+=g;
            g=a[j]/10;
            a[j]%=10;
            */
            if(a[j]>=10)
            {
                for(int k=0;k<len;k++)
                {
                    if (a [len- 1 ]> = 10 ) len ++ ;
                    a[k+1]+=a[k]/10;
                    a[k]%=10;
                }
            }
        }
        //while(g) a[len++]+=g,g/=10; 
    }
    for(int i=len-1;i>=0;i--) cout<<a[i];
    return 0;
}