'''lecture_34_factorial.py
The factorial function computed using recursion
Oliver W. Layton
CS 151: Computational Thinking: Visual Media
Spring 2021
'''


def factorial(n):
    '''n is an int >=0 that we are taking the factorial of
    e.g. factorial(4) = 4*factorial(3)
    '''
    if n == 0:
        # Base case: where the recursion stops / where
        # we stop calling the function from within the function.
        # always needed when using recursion (otherwise you will
        # keep calling function from within the function
        # infinitely many times!)
        ans = 1
    else:
        ans = n*factorial(n-1)
    return ans


if __name__ == '__main__':
    answer = factorial(3) 
    # factorial(3) = 3*2*1 = 6
    # answer = factorial(4)
    # factorial(4) = 4*3*2*1 = 24
    # answer = factorial(12)
    print(answer)