Transform String - KOTLIN

// Author : Saurav Kalsoor
// Transform String - KOTLIN

import java.util.*


var sc: Scanner = Scanner(System.`in`)

fun main() {
    val str: String = sc.next()
    println(transformString(str))
}

fun transformString(str: String): String? {
    if (str.length == 2) return str
    val n = str.length
    var newStr = ""
    var i = 0
    while (i < n) {
        newStr += if (i == n - 1) {
            str[i]
        } else {
            getAverage(str[i], str[i + 1])
        }
        i += 2
    }
    return transformString(newStr)
}

fun getAverage(a: Char, b: Char): Char {
    val avg = (a - 'a' + (b - 'a')) / 2
    return (avg + 'a'.code).toChar()
}