12.3 Recursion with strings and lists

Learning objectives

By the end of this section you should be able to

Demonstrate the use of recursion to solve a string problem.
Demonstrate the use of recursion to solve a list problem.
Use the built-in count() list function.

Recursion with strings

A word that is spelled the same forward and backward is called a palindrome. Ex: racecar.

Recursion can be used to identify whether a given word is a palindrome.

Recursion with lists

The animation below shows a recursive way to check whether two lists contain the same items but in different order.

The count() function returns a count of the number of items in a list that match the given item, and returns 0 otherwise. Ex: For list_num = [1, 3, 3, 4], list_num.count(3) returns 2.

Try It

Remove duplicates

Write a recursive rem_dup() function that removes duplicates from a list.

Ex: List [5, 5, 2, 1, 3, 1, 6] should result in an output list [5, 2, 1, 3, 6].

def rem_dup(list_1, list_2=[]): # Second default parameter
# Your code here

test_list = [5, 5, 2, 1, 3, 1, 6]
print(rem_dup(test_list))

Adapted from Introduction to Python Programming by OpenStax (openstax.org), licensed under CC BY-NC-SA 4.0. Changes were made. License: CC-BY-NC-SA-4.0.