var prevResult = "abcde"
var tmp = prevResult[0]

for (i in 0..prevResult.length - 2) {
    prevResult[i] = prevResult[i+1]  // Error on preveResult[i]
}

prevResult[prevResult.length-1] = tmp // Error on preveResult[prevResult.lengt-1]

var prevResult = "abcde"
var tmp = prevResult[0]

var builder = StringBuilder()

for (i in 0..prevResult.length - 2) {
  builder.append(prevResult[i+1])
}

builder.append(tmp)  // Don't really need tmp, use prevResult[0] instead.
var result = builder.toString()

var result = prevResult.substring(1) + prevResult[0]

var result = prevResult.drop(1) + prevResult.take(1)

val str = "abcde"
val r1 = str.drop(1) + str.first()
val r2 = str.drop(1) + str.take(1)

val r1 = str.toCharArray().let {
    for (i in 0..it.lastIndex - 1)
        it[i] = it[i+1]
    it[it.lastIndex] = str[0] // str is unchanged
    String(it)
}

fun String.rotate(n: Int) = drop(n % length) + take(n % length)

val str = "abcde"
val r1 = str.rotate(1)

val chars = input.toMutableList()
val temp = chars[posA]
chars[posA] = chars[posB]
chars[posB] = temp
return chars.joinToString(separator = "")