Given a positive integer, N. Find the factorial of N.
Example 1:
Input:
N = 5
Output:
120
Explanation:
5*4*3*2*1 = 120
Example 2:
Input:
N = 4
Output:
24
Explanation:
4*3*2*1 = 24
Your Task: You don't need to read input or print anything. Your task is to complete the function factorial() which takes an integer N as input parameters and returns an integer, the factorial of N.
Expected Time Complexity: O(N)
Expected Space Complexity: O(N)