Factorial

Version1:
Recursive version

def factorial(n):
    if n == 0: return 0
    if n == 1: return 1
    if n > 2:
        return n * factorial(n-1)

Memoization of factorial function:

mem= {}
def factorial(n):
    if n == 0: return 0
    if n == 1: return 1
    if n > 2:
        mem[n] = n * factorial( n-1)
    return mem