623 - 500!

Problem Link : https://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&page=show_problem&problem=564

Solution Idea : have to find factorial n with efficient method.

Solution :

#include<bits/stdc++.h>
#define ll long long
using namespace std;

#define MAX 10000

ll int res[MAX];

ll int multiply(ll int x,ll int res_size);

void factorial(ll int n)
{


    res[0] = 1;
    ll int res_size = 1;

    for (ll int x=2; x<=n; x++)
        res_size = multiply(x, res_size);


    for (ll int i=res_size-1; i>=0; i--)
        printf("%lld",res[i]);
        printf("\n");
}

ll int multiply(ll int x,ll int res_size)
{
   ll int carry = 0;

       for (ll int i=0; i<res_size; i++)
    {
        ll int prod = res[i] * x + carry;
        res[i] = prod % 10;
        carry  = prod/10;
    }

    while (carry)
    {
        res[res_size] = carry%10;
        carry = carry/10;
        res_size++;
    }
    return res_size;
}


int main()
{
    ll int n;

    while(scanf("%lld",&n)==1)
    {
        printf("%lld!\n",n);
        factorial(n);
    }

    return 0;

}