Anonymous Kotlin function: Check palindrome string

Last update on August 27 2025 12:42:46 (UTC/GMT +8 hours)

Write an anonymous Kotlin function to check if a string is a palindrome.

Pre-Knowledge (Before You Start!)

Before solving this exercise, you should be familiar with the following concepts:

Anonymous Functions: An anonymous function is a function that is defined without a name, often used for short operations.
String Manipulation: Functions like toLowerCase() and replace() allow you to modify strings. toLowerCase() converts a string to lowercase, while replace() can remove unwanted characters using regular expressions.
Reversing Strings: The reversed() function reverses the order of characters in a string.
Regex: Regular expressions help in pattern matching and replacing specific characters in a string. In this case, we remove all non-alphanumeric characters.

Hints (Try Before Looking at the Solution!)

Here are some hints to help you solve the problem:

Hint 1: Create an anonymous function that takes a string as an argument and returns a Boolean.
Hint 2: To ignore case sensitivity, convert the string to lowercase.
Hint 3: Use a regular expression in replace() to remove any non-alphanumeric characters.
Hint 4: Compare the cleaned string with its reversed version using the reversed() function.
Hint 5: Return true if the string is a palindrome, otherwise return false.

Sample Solution:

Kotlin Code:

fun main() {
    val isPalindrome: (String) -> Boolean = { str ->
        val cleanStr = str.lowercase().replace(Regex("[^a-zA-Z0-9]"), "")
        cleanStr == cleanStr.reversed()
    }

    val str1 = "Madam"
    val str2 = "Kotlin"

    println("$str1 is a palindrome: ${isPalindrome(str1)}")
    println("$str2 is a palindrome: ${isPalindrome(str2)}")
}

Sample Output:

Madam is a palindrome: true
Kotlin is a palindrome: false

Explanation:

In the above exercise -

Inside "main()" function we define an anonymous function isPalindrome with the type (String) -> Boolean. This function takes a single string argument and returns a Boolean indicating whether the string is a palindrome or not.

The isPalindrome function implements the following steps:

It converts the input string to lowercase using toLowerCase() to ignore case sensitivity.
It removes any non-alphanumeric characters from the string using replace(Regex("[^a-zA-Z0-9]"), "").
It checks if the cleaned string is equal to its reversed version using the == operator.
The result of the equality comparison is returned as a Boolean value.

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