Question

PYTHON PYTHON

Recursive Functions. In this problem, you are asked to write three recursive functions. Implement all functions in a module called problem1.py.

1. (10 points) Write a recursive function called remove char with two parameters: a string astr and a character ch. The function returns a string in which all occurrences of ch in astr are removed. For example, remove char("object oriented", ’e’) returns the string "objct orintd". Your implementation should not contain any loops and may use only the index [] and slice operators [:] for strings. No other built-in functions may be used.

2. (10 points) Write a recursive function called occurrences with two parameters: a string astr and another (nonempty) string substr. The function returns the number of times the substring substr appears in the string astr. For example, occurrences("how now brown cow", "ow") should return 4, occurrences("house mouse louse", "ow") should return 0, and occurrences("green eggs and ham", "egg") should return 1. Your implementation should not contain any loops and may use only the index [] and slice operators [:] for strings. No other built-in functions may be used. Please note that in is a built-in function, and you may not use it to implement your function.

3. (10 points) Write a recursive function called duplicates with a single parameter L, a list of items. The function returns True if L has any duplicate (i.e. repeating) items and False otherwise. The function must be implemented recursively. The base case occurs when the list is empty (in which case it returns False). Your function should consist only of the base case and recursive calls in an if/else statement. You are not allowed to use any built-in functions other than len for lists. Please note that in is a built-in function, and you may not use it to implement your function. In addition, you are only allowed to use the index operator [] and the slice operator [:] for lists. There should not be any loops (for or while) in your implementation! Hint: Your function will need two recursive calls, not just one.

Answer 1

ANSWER:

Program 1

# recursive method to remove occurances of character from string

def remove_char(astr, ch):

# if string is empty return

if not astr:

return ""

# check the first char

if astr[0] == ch:

return remove_char(astr[1:], ch)

# add the first character and recur the method

return astr[0] + remove_char(astr[1:], ch)

#call the above method

print(remove_char('object oriented','e'))

Screesnhot

Output

Program 2

# method which returns the number of occurrences of str2 in str1

def occurrences(str1, str2):

# find the length of strings

n1 = len(str1)

n2 = len(str2)

# consition to exit the recursion

if n1 == 0 or n1 < n2:

return 0

# check if the string matches

if str1[: n2] == str2:

return occurrences(str1[n2 - 1:], str2) + 1

return occurrences(str1[n2 - 1:], str2)

#call the above methods

print(occurrences("green eggs and ham","egg"))

Screenshot

Output

Program

#method to check if a ist has duplicates

def duplicates(L):

#if list is empty retusn false

if len(L) <= 1:

return False

#now check first and second elements

if L[0] == L[1]:

return True

#call the method with first element and rest

if duplicates([L[0]] + L[2:]):

return True

if duplicates(L[1:]):

return True

#if we reach the end , retusn False

return False

#call the above method

print(duplicates([1,2,5,3,4,2]))

Screenshot

Output

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