Skip to main content

How to reverse a LinkedList in Kotlin

How to reverse a LinkedList in Kotlin.

Here's a step-by-step tutorial on how to reverse a LinkedList in Kotlin:

Step 1: Create the LinkedList class​

First, we need to create a class for the LinkedList. This class will have two properties: the head (which points to the first node in the list) and the tail (which points to the last node in the list). We'll also define a function to add nodes to the list.

class LinkedList {
    var head: Node? = null
    var tail: Node? = null

    class Node(var data: Int) {
        var next: Node? = null
    }

    fun addNode(data: Int) {
        val newNode = Node(data)
        if (head == null) {
            head = newNode
            tail = newNode
        } else {
            tail?.next = newNode
            tail = newNode
        }
    }
}

Step 2: Create the reverse function​

Next, we'll create a function called reverse that will reverse the LinkedList. This function will iterate through the list and update the next pointers of each node to reverse the order.

fun reverse(list: LinkedList) {
    var prev: LinkedList.Node? = null
    var current = list.head
    var next: LinkedList.Node?

    while (current != null) {
        next = current.next
        current.next = prev
        prev = current
        current = next
    }

    list.head = prev
}

Step 3: Test the reverse function​

To test the reverse function, we'll create a sample LinkedList, add some nodes, and then call the reverse function. Finally, we'll print the reversed LinkedList to verify the result.

fun main() {
    val list = LinkedList()
    list.addNode(1)
    list.addNode(2)
    list.addNode(3)
    list.addNode(4)
    list.addNode(5)

    println("Original LinkedList:")
    printLinkedList(list)

    reverse(list)

    println("Reversed LinkedList:")
    printLinkedList(list)
}

fun printLinkedList(list: LinkedList) {
    var current = list.head
    while (current != null) {
        print("${current.data} ")
        current = current.next
    }
    println()
}

When you run the above code, you should see the following output:

Original LinkedList:
1 2 3 4 5 
Reversed LinkedList:
5 4 3 2 1

That's it! You have successfully reversed a LinkedList in Kotlin.