Delete odd nodes from linked list in kotlin

Kotlin program for Delete odd nodes from linked list. Here problem description and explanation.

// Kotlin program for
// Delete odd nodes from linked list

// Node of Linked List
class LinkNode
{
	var data: Int;
	var next: LinkNode ? ;
	constructor(data: Int)
	{
		//Set node value
		this.data = data;
		this.next = null;
	}
}
class SingleLL
{
	var head: LinkNode ? ;
	var tail: LinkNode ? ;
	constructor()
	{
		this.head = null;
		this.tail = null;
	}
	// Add new node at the end of linked list
	fun addNode(value: Int): Unit
	{
		// Create a new node
		val node: LinkNode = LinkNode(value);
		if (this.head == null)
		{
			this.head = node;
		}
		else
		{
			this.tail?.next = node;
		}
		this.tail = node;
	}
	// Display linked list element
	fun display(): Unit
	{
		if (this.head == null)
		{
			return;
		}
		var temp: LinkNode ? = this.head;
		// iterating linked list elements
		while (temp != null)
		{
			print(""+ temp.data + " → ");
			// Visit to next node
			temp = temp.next;
		}
		print("null\n");
	}
	// Delete all odd key nodes in linked list
	fun deleteOddNodes(): Unit
	{
		// Define some auxiliary variables
		var current: LinkNode ? = this.head;
		var auxiliary: LinkNode ? = null;
		var back: LinkNode ? = null;
		// iterating linked list elements
		while (current != null)
		{
			if ((current.data % 2) != 0)
			{
				// When get odd node
				auxiliary = current;
			}
			else
			{
				back = current;
			}
			// Visit to next node
			current = current.next;
			if (auxiliary != null)
			{
				// When Deleted node exists
				if (back == null)
				{
					// When front node is odd node
					// head visit to next node
					this.head = current;
				}
				else
				{
					// When deleting centralized node
					back.next = current;
				}
				if (this.tail == auxiliary)
				{
					// When delete last node
					// Set new tail
					this.tail = back;
				}
				// Unlink deleted node 
				auxiliary.next = null;
				auxiliary = null;
			}
		}
	}
}
fun main(args: Array < String > ): Unit
{
	val sll: SingleLL = SingleLL();
	// Add linked list node
	sll.addNode(3);
	sll.addNode(1);
	sll.addNode(4);
	sll.addNode(7);
	sll.addNode(9);
	sll.addNode(6);
	sll.addNode(5);
	sll.addNode(11);
	// Before effect
	println("Before Delete Odd Key Nodes");
	// 3 → 1 → 4 → 7 → 9 → 6 → 5 → 11 → NULL
	sll.display();
	// Perform delete operation
	sll.deleteOddNodes();
	// After effect
	println("After Delete Odd Key Nodes");
	// 4 → 6 → NULL
	sll.display();
}

Output

Before Delete Odd Key Nodes
3 → 1 → 4 → 7 → 9 → 6 → 5 → 11 → null
After Delete Odd Key Nodes
4 → 6 → null