kotlin - palindrome test - 3 implementations: string reversed, stack, stack with size optimized

palindrome_test.kt

import kotlin.collections.ArrayDeque

// version #1 - the shortest implementation
// fun checkPalindrome(word: String): Boolean = word.reversed() == word

// version #2 - 'pure stack' implementation
/*
fun checkPalindrome(word: String): Boolean {
    if (word.isBlank())
        return false

    val stack: ArrayDeque<Char> = ArrayDeque(word.length)
    word.forEach(stack::addFirst)
    word.forEach {
        if (it != stack.removeFirst())
            return false
    }
    return true
}
*/

// version #3 - stack implementation with stack size optimization
fun checkPalindrome(word: String): Boolean {
    if (word.isBlank()) return false

    val wordHalfLen: Int = word.length / 2 + word.length % 2
    val word2ndHalfStartIndx = word.length - wordHalfLen
    val stack: ArrayDeque<Char> = ArrayDeque(wordHalfLen)

    word.forEachIndexed { i, c ->
        // only 1st half of the word is pushed on the stack
        if (i < wordHalfLen) {
            stack.addFirst(c)
        }

        // and the 2nd half is compared against the stack
        if (i >= word2ndHalfStartIndx && c != stack.removeFirst()) {
            return false
        }
    }
    return true
}

fun main() {
    val input = readln()
    println(checkPalindrome(input))
}