Python Program to Check Whether a String is a Palindrome or not Using Recursion

A palindrome is a string that reads the same forwards and backwards, such as "racecar" or "madam". We can check if a string is a palindrome using recursion by comparing characters from both ends and recursively checking the substring in between.

Recursion works by breaking down the problem into smaller subproblems. For palindrome checking, we compare the first and last characters, then recursively check the remaining substring until we reach the base case.

Syntax

The recursive approach follows this logic ?

def check_palindrome(string):
    if len(string) <= 1:
        return True
    if string[0] == string[-1]:
        return check_palindrome(string[1:-1])
    else:
        return False

Example

Here's a complete program to check if a string is a palindrome using recursion ?

def check_palindrome(my_str):
    if len(my_str) <= 1:
        return True
    else:
        if my_str[0] == my_str[-1]:
            return check_palindrome(my_str[1:-1])
        else:
            return False

# Test with different strings
test_strings = ["racecar", "hello", "madam", "python"]

for string in test_strings:
    if check_palindrome(string):
        print(f"'{string}' is a palindrome")
    else:
        print(f"'{string}' is not a palindrome")

'racecar' is a palindrome
'hello' is not a palindrome
'madam' is a palindrome
'python' is not a palindrome

How It Works

The recursive function works as follows ?

• Base case: If the string length is 0 or 1, it's automatically a palindrome
• Comparison: Compare the first character my_str[0] with the last character my_str[-1]
• Recursive call: If they match, recursively check the substring my_str[1:-1] (excluding first and last characters)
• Return False: If characters don't match, the string is not a palindrome

Case-Insensitive Palindrome Check

To handle cases like "Racecar", we can make the check case-insensitive ?

def check_palindrome_ignore_case(my_str):
    my_str = my_str.lower()  # Convert to lowercase
    if len(my_str) <= 1:
        return True
    else:
        if my_str[0] == my_str[-1]:
            return check_palindrome_ignore_case(my_str[1:-1])
        else:
            return False

# Test with mixed case strings
test_strings = ["Racecar", "Level", "Hello", "Madam"]

for string in test_strings:
    if check_palindrome_ignore_case(string):
        print(f"'{string}' is a palindrome (ignoring case)")
    else:
        print(f"'{string}' is not a palindrome")

'Racecar' is a palindrome (ignoring case)
'Level' is a palindrome (ignoring case)
'Hello' is not a palindrome
'Madam' is a palindrome (ignoring case)

Conclusion

Recursive palindrome checking compares characters from both ends and processes the middle substring recursively. This approach elegantly handles the problem by reducing it to smaller subproblems until reaching the base case.