Delete middle node from linked list in kotlin

Kotlin program for Delete middle node from linked list. Here problem description and explanation.

/*
    Kotlin program for
    Delete middle node of linked list
*/
// Linked list node
class LinkNode
{
	var data: Int;
	var next: LinkNode ? ;
	constructor(data: Int)
	{
		this.data = data;
		this.next = null;
	}
}
class SingleLL
{
	var head: LinkNode ? ;
	constructor()
	{
		this.head = null;
	}
	// Adding new node at beginning of linked list
	fun addNode(data: Int): Unit
	{
		// Create new node
		val node: LinkNode = LinkNode(data);
		// Connect current node to previous head
		node.next = this.head;
		this.head = 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)
		{
			// Display node value
			print(""+ temp.data + " → ");
			// Visit to next node
			temp = temp.next;
		}
		print(" NULL\n");
	}
	// Delete the middle node of linked list
	fun deleteMid(): Unit
	{
		if (this.head == null)
		{
			// When linked list are no elements
			println("Empty Linked List");
		}
		else if (this.head?.next == null && 
                 this.head?.next?.next == null)
		{
			// When linked list are less than  of 3 nodes
			println("Less then 3 node of linked list");
		}
		else
		{
			var temp: LinkNode ? = this.head;
			var midPrevious: LinkNode ? = null;
			// Find the middle and its previous node
			while (temp != null && temp.next != null && 
              temp.next?.next != null)
			{
				if (midPrevious == null)
				{
					// When first node
					midPrevious = temp;
				}
				else
				{
					// Visit to next node
					midPrevious = midPrevious.next;
				}
				// Visit to next second next node
				temp = temp.next?.next;
			}
			// Get the node which is deleting 
			temp = midPrevious?.next;
			// Show deleted node
			println("Delete node : " + temp!!.data);
			// Change link
			midPrevious?.next = temp.next;
		}
	}
}
fun main(args: Array < String > ): Unit
{
	val sll: SingleLL = SingleLL();
	// Linked list
	// 7 → 6 → 5 → 4 → 3 → 2 → 1 → NULL
	sll.addNode(1);
	sll.addNode(2);
	sll.addNode(3);
	sll.addNode(4);
	sll.addNode(5);
	sll.addNode(6);
	sll.addNode(7);
	println("Before Delete middle node");
	sll.display();
	// Delete middle node
	sll.deleteMid();
	println("After Delete middle node");
	sll.display();
}

Output

Before Delete middle node
7 → 6 → 5 → 4 → 3 → 2 → 1 →  NULL
Delete node : 4
After Delete middle node
7 → 6 → 5 → 3 → 2 → 1 →  NULL


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