Calculate Factorial of a Number

Given a non-negative integer n, calculate and return its factorial modulo 1,000,000,007.

The factorial of a number is the product of all positive integers less than or equal to that number.

Mathematically:

n! = n * (n - 1) * (n - 2) * ... * 2 * 1

The factorial of zero is defined as 1. Therefore, 0! = 1 and 1! = 1.

Since factorial values grow very quickly, return the result modulo 1,000,000,007. This means returning the remainder after dividing n! by 1,000,000,007.

For example, 5! = 120, so the result for n = 5 is 120.

Implement the function factorial(n) that returns the factorial modulo 1,000,000,007.

0 <= n <= 100000