Factorial

Given a non-negative integer n, return the factorial of n.

The factorial of n is the product of all positive integers less than or equal to n. By definition, 0! = 1.

Example 1:

Input: n = 5
Output: 120
Explanation: 5! = 5 × 4 × 3 × 2 × 1 = 120

Example 2:

Input: n = 0
Output: 1
Explanation: 0! = 1 by definition

Constraints:

• 0 <= n <= 12