Day 70: Python Program to Determine How Many Times a Given Letter Occurs in a String Recursively

 

def count_letter_recursively(s, letter):

    if not s:

        return 0

    return (1 if s[0] == letter else 0) + count_letter_recursively(s[1:], letter)

input_string = input("Enter a string: ")

input_letter = input("Enter the letter to count: ")

if len(input_letter) != 1:

    print("Please enter only one letter.")

else:

    count = count_letter_recursively(input_string, input_letter)

    print(f"The letter '{input_letter}' occurs {count} times in the string.")

#source code --> clcoding.com 

Code Explanation:

Function Definition

def count_letter_recursively(s, letter):

Purpose: Defines a function named count_letter_recursively.

Parameters:

s: A string in which the letter is counted.

letter: The specific letter to count within the string.

    if not s:

        return 0

Logic: Checks if the string s is empty (base case of recursion).

If s is empty, it returns 0 because there are no letters left to count.

    return (1 if s[0] == letter else 0) + count_letter_recursively(s[1:], letter)

Logic: Processes the first character of the string (s[0]):

If s[0] matches the letter, it adds 1 to the count.

Otherwise, adds 0.

Recursively calls count_letter_recursively on the rest of the string (s[1:]), effectively reducing the problem size by one character each time.

Input Handling

input_string = input("Enter a string: ")

Purpose: Prompts the user to enter a string and stores it in the variable input_string.

input_letter = input("Enter the letter to count: ")

Purpose: Prompts the user to enter the specific letter to count and stores it in input_letter.

Validation and Execution

if len(input_letter) != 1:

    print("Please enter only one letter.")

Logic: Checks if the user entered more than one character as the letter.

If input_letter is not exactly one character long, it prints an error message and exits.

else:

    count = count_letter_recursively(input_string, input_letter)

Logic: If the input is valid, it calls count_letter_recursively with the input_string and input_letter.

Result: The result of the function (number of occurrences) is stored in the variable count.

    print(f"The letter '{input_letter}' occurs {count} times in the string.")

Purpose: Prints the result, displaying how many times the letter appears in the input string.