Panda and Chain Reaction

Panda has become a scientist recently. In his laboratory, there are infinite number of chambers where a chamber number K is connected to a chamber number K-1.

The numbering of chambers start from 0. Initially, X number of particles are present in the chamber number 0. The number of particles present in chamber K is K times the number of particles present in chamber K-1. You are supposed to help Panda in finding out the number of particles in a given chamber number N.

Note: The number of particles in chamber K cannot be calculated until the number of particles in chamber K-1 are calculated.

Example:

Input:  n = 1, x = 3
Output: 3

Approach

C++

#include <bits/stdc++.h>
using namespace std;
#define MOD 1000003

long long arr[1000004];
void initialize()
{

    arr[0] = 0;
    arr[1] = 1;
    for (long long i = 2; i < 1000004; i++)
        arr[i] = ((arr[i - 1] % MOD) * (i % MOD)) % MOD;
}
long long chainReaction(long long n, long long x)
{
    long long ans;
    if (n >= MOD)
        ans = 0;
    else
        ans = (arr[n] * x) % MOD;
    return ans;
}
int main()
{
    initialize();
    long long n = 1, x = 3;

    cout << chainReaction(n, x) << "\n";

    return 0;
}