Question

Python.

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

Important notes:

• If e is not an element of s, the function should return -1.

• You may not use the in operator in this function. In addition, you may not use your num_occur function or any other helper function except the len function.

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

Answer 1

• Below is the detailed implementation of the above problem in python with code and output.
• Please read the comments mentioned in the code for better understanding.
• CODE:

#function which returns the last index in s where s[index]=e
def last_occur(s, e):
#if length of s is 0 then return -1 i.e, not found e
if len(s)==0:
return -1
#if last character/element of s is e then return length of s - 1.
if s[-1]==e:
return len(s)-1
#otherwise call last_occur() recursively for s without last element/character i.e, s[:-1]
else:
return last_occur(s[:-1], e)
#test case 1
print(last_occur("abcdbefefefeeg","f"))

#test case 2
print(last_occur("abcdbefefefeeg","h"))

#test case 3
print(last_occur([1,2,3,4,5,6,7,6,5,4,3,2,1],"f"))

#test case 4
print(last_occur([1,2,3,4,5,6,7,6,5,4,3,2,1],7))

• OUTPUT:

1. 10

2. -1

3. -1

4. 6

• For better understanding below are the screenshot attached for the code and output.

CODE and INPUT/OUTPUT

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