Authors:
Y Daniel Lang
Chapter:
5.recursion
Exercise:
Programming Excercises
Question:16 | ISBN:978013274719 | Edition: 6
Question
(Occurrences of a specified character in a list) Write a recursive function that finds the number of occurrences of a specified character in a list. You need to define the following two functions. The second one is a recursive helper function.
def count(chars, ch):
def countHelper(chars, ch, high):
Write a test program that prompts the user to enter a list of characters in one line, and a character, and displays the number of occurrences of the character in the list.
Answer
Python code:
# Recursive function to count the occurrences of
#a specified character in a list.
def count(chars, ch):
return countHelper(chars, ch, len(chars) - 1)
#Recursive helper function to count the
#occurrences of a specified character in a list.
def countHelper(chars, ch, high):
# Base case: If we have reached the beginning of the list, return 0.
if high < 0:
return 0
# Recursive case: Count the occurrences of the character in the sublist
# from index 0 to high-1, and add 1 if the character at
#the high index matches the specified character.
count = countHelper(chars, ch, high - 1)
if chars[high] == ch:
count += 1
return count
# Prompt the user for input
char_list = list(input("Enter a list of characters in one line: "))
char = input("Enter a character to count: ")
# Count the occurrences of the character in the list
occurrences = count(char_list, char)
# Display the result
print(f"The number of occurrences of '{char}' in the list is: {occurrences}")
Executed Output:
Enter a list of characters in one line: hello Python world
Enter a character to count: o
The number of occurrences of 'o' in the list is: 3