Recursive Index

Whiteboard: Medium
Challenge: Easier
Concepts: Recursion
Download: recursive-index.zip
Solution: Recursive Index: Solution

Find the index of an item in a list using recursion.

Given a list of items:

>>> lst = ["hey", "there", "you"]

You should have a function that returns the 0-based index of a sought item:

>>> recursive_search("hey", lst)
0

>>> recursive_search("you")
2

If the item isn’t in the list, return None:

>>> recursive_search("porcupine", lst) is None
True

Important: Solve this problem only with recursion—you cannot use a for or while loop in your solution!

We’ve given you a file, recursiveindex.py, with an empty function, recursive_index:

def recursive_index(needle, haystack):
    """Given list (haystack), return index (0-based) of needle in the list.

    Return None if needle is not in haystack.

    Do this with recursion. You MAY NOT USE A `for` OR `while` LOOP.
    """

Implement this method.