Python Recursion Factorial Example

python_recursion_factorial_example.py

'''
Recursion can be difficult for beginners. It still is difficult for me.
The best way to improve is to try "easy" recursion problems such as 
factorials in this case. 

Instructions: 
Create a function that takes an positive interger and returns the factorial of it
Example factorial(3) should return 3*2*1 or 6 
Factorial(1) should return 1
Factorial(0) should return 1
''' 

#Non Recursion Example
def factorial(x):
    total = 1
  if x == 0 or x == 1:  # Handles Edge Case of 1 or 0
    return total
  while x > 1: 
    total = total * x # Multiples variable total defined outside of loop with x
    x-=1 # Subtracts one from x so that the while loop will break when x = 1
  return total 

# Recursion Example
def factorial(x):
  if x == 0 or x ==1: # When x is equal to 0 or 1, it returns 1
    return 1
  return x * factorial(x-1) # multiples x with the recursion or calling itself with x - 1
'''  
If we do factorial (3)
It first checks if x is == 0 or x == 1 => False
  Then it go to x * factorial(x-1) which would be 3 * factorial(2)
    Evaluate factorial(2)
      Check if x == 0 or x == 1 => False
        x * factorial(x-1) or 2 * factorial(1)
          Evaluates factorial(1) 
            Check if x == 0 or x == 1 => True
            returns 1
          factorial(1) evaluates to 1 
          returns 1
        So 2 * factorial(1) = 2 * 1 => 2
        factorial(2) evaluates to 2
        returns 2
    So factorial(2) = 2
  So 3 * factorial(2) = 3 * 2 => 6
This function then returns 6
'''