Recursion assignment

Question

def swap(aList):

  if len(aList) == 0:
      return 0
  elif len(aList) == 1:
      print(aList[0])
      return aList[0]
  return aList[0] + swap(aList[2:])

aList = [         


        

Answer 1

Whenever you have a recursion problem, you need to ask yourself two questions:

1. What is the base case (the simplest possible case). There can be more than one.
2. If I'm not in the base case, how can I write some code that calls the current function in a case closer to the base case.

In your case, the base case seems to be correct, but what you're returning doesn't seem to be correct for len==0. If a string is length zero, what would you be returning?

Your second base case looks fine, but you shouldn't mix printing and returning. Just return the aList[0], and then you can print out the output from calling your swap function.

For your recursive case, think about just the string "ab" - how do you get the recursive call to return "ba."