Detect loop of the given LinkedList

DetectLoopLinkedList.kt

class LinkedListNode(var next: LinkedListNode?, val value: String)

fun detectLoop(list: LinkedListNode): String {
    var node1 = list
    var node2 = list
    var n = 0
    do {
        node1 = node1.next!!
        node2 = node2.next!!.next!!
        n++
    } while (node1 != node2)

    node1 = list
    node2 = list
    while (n > 0) {
        node2 = node2.next!!
        n--
    }

    while (node1 != node2) {
        node1 = node1.next!!
        node2 = node2.next!!
    }
    return node1.value
}

fun main() {
    println(detectLoop(build(2, 3))) // A -> B -> C -> D -> E -> C
    println(detectLoop(build(3, 2))) // A -> B -> C -> D -> E -> D
    println(detectLoop(build(1, 1))) // A -> B -> B
    println(detectLoop(build(1, 5))) // A -> B -> C -> D -> E -> F -> B
    println(detectLoop(build(4, 2))) // A -> B -> C -> D -> E -> F -> E
    println(detectLoop(build(5, 1))) // A -> B -> C -> D -> E -> F -> F
}

fun build(i: Int, L: Int): LinkedListNode {
    val last = LinkedListNode(null, ('A' + i + L).toString())
    var list = last
    repeat(i + L - 1) { idx ->
        list = LinkedListNode(list, ('A' + i + L - idx - 1).toString())
    }
    var node = list
    repeat(i - 1) {
        node = node.next!!
    }
    last.next = node
    return list
}