Question

Python

Write a function index_last(elem, seq) that takes as inputs an element elem and a sequence seq, and that uses recursion (i.e., that calls itself recursively) to find and return the index of the last occurrence of elem in seq. The sequence seq can be either a list or a string. If seq is a string, elem will be a single-character string; if seq is a list, elem can be any value. Don’t forget that the index of the first element in a sequence is 0.

Important notes:

• If elem is not an element of seq, the function should return -1.

• You may not use the in operator in this function.

• Your index_last function must call itself recursively. You must not write a separate helper function to perform the recursion.

Here are some examples:

>>> index_last(5, [4, 10, 5, 3, 7, 5])
result: 5

>>> index_last('hi', ['well', 'hi', 'there'])
result: 1

>>> index_last('b', 'banana')
result: 0

>>> index_last('n', 'banana')
result: 4

>>> index_last('i', 'team')
result: -1

>>> index_last('hi', ['hello', 111, True])
result: -1

>>> index_last('a', '')    # the empty string 
result: -1

>>> index_last(42, [])     # the empty list
result: -1

Hints:

• You will need more than one base case for this function.

• When making the recursive call, it will be helpful to take a different approach than we’ve typically taken when recursively processing a string. Ask yourself: How could I reduce the problem in such a way that I could easily find the last occurrence of elem in seq?

• Here again, we encourage you to begin by considering concrete cases. Ask yourself the types of design questions that we have asked in lecture and lab, and use the answers to those questions to determine what the function should do.

Answer 1

Explanation::

• Code in PYTHON is given below
• Please read comments for better understanding of the code
• Output is given at the end of the code

Code in PYTHON::

'''
Base Case 1: First condition we check is if length of seq is 0 or no
    If 0 then we return -1
Base Case 2: Check if last element of the seq is equal to elem.
    If yes then return the index of last element of th seq
Base Case 3: If element in seq is the only one element then we return -1
    as base case 2 is false.
Base Case 4:
    We call the function index_last() recursively by passing
    the elem and seq without last element 
'''
def index_last(elem,seq):
    if len(seq)==0:
        return -1
    elif seq[len(seq)-1]==elem:
        return len(seq)-1
    elif len(seq)-1==0:
        return -1
    else:
        return index_last(elem,seq[0:len(seq)-1])

print(index_last(5,[4,10,5,3,7,5]))
print(index_last('hi',['well','hi','there']))
print(index_last('b','banana'))
print(index_last('n','banana'))
print(index_last('i','team'))
print(index_last('hi',['hello',111,True]))
print(index_last('a',''))
print(index_last(42,[]))

SCREENSHOT OF THE CODE:

OUTPUT:

Please provide the feedback!!

Thank You!!