Fold linked list in c#

Csharp program for Fold linked list. Here problem description and other solutions.

// Include namespace system
using System;
/*
  Csharp program for
  Fold linked list
*/
// Linked list node
public class LinkNode
{
	public int data;
	public LinkNode next;
	public LinkNode(int data)
	{
		this.data = data;
		this.next = null;
	}
}
public class SingleLL
{
	public LinkNode head;
	public SingleLL()
	{
		// Set initial value
		this.head = null;
	}
	// Add node at the beginning
	public void addNode(int data)
	{
		// Create new node
		var node = new LinkNode(data);
		node.next = this.head;
		// Set new head
		this.head = node;
	}
	// Display linked list element
	public void display()
	{
		if (this.head == null)
		{
			return;
		}
		var temp = this.head;
		// iterating linked list elements
		while (temp != null)
		{
			Console.Write(" " + temp.data + " →");
			// Visit to next node
			temp = temp.next;
		}
		Console.WriteLine(" NULL");
	}
	// This is handle the request of 
	// folding given linked list nodes
	public void foldList()
	{
		if (this.head == null)
		{
			Console.Write("\n Empty linked list");
			return;
		}
		// Some auxiliary variables
		var temp = this.head;
		var auxiliary = this.head;
		LinkNode hold = null;
		// Loops used to find the middle node
		while (temp != null && 
               temp.next != null && 
               temp.next.next != null)
		{
			// Visit to next node
			auxiliary = auxiliary.next;
			// Visit to second next node
			temp = temp.next.next;
		}
		if (auxiliary != null)
		{
			hold = auxiliary;
			auxiliary = auxiliary.next;
			// Separating half nodes
			hold.next = null;
			// Start with first node of next half section
			temp = auxiliary;
			auxiliary = null;
			// Reverse second half nodes 
			while (temp != null)
			{
				hold = temp;
				temp = temp.next;
				hold.next = auxiliary;
				auxiliary = hold;
			}
			// Start with first node of linked list
			temp = this.head;
			// Combine first and second half nodes 
			// in alternate manner
			while (temp != null)
			{
				hold = temp;
				temp = temp.next;
				hold.next = auxiliary;
				if (auxiliary != null)
				{
					hold = auxiliary;
					auxiliary = auxiliary.next;
					hold.next = temp;
				}
			}
		}
	}
	public static void Main(String[] args)
	{
		// Create a empty linked lists
		var sll1 = new SingleLL();
		var sll2 = new SingleLL();
		//  Constructed first linked list
		//  1 → 2 → 3 → 4 → 5 → 6 → 7 → 8 → NULL
		sll1.addNode(8);
		sll1.addNode(7);
		sll1.addNode(6);
		sll1.addNode(5);
		sll1.addNode(4);
		sll1.addNode(3);
		sll1.addNode(2);
		sll1.addNode(1);
		// Constructed second linked list
		//  1 → 2 → 3 → 4 → 5 → 6 → 7 → NULL
		sll2.addNode(7);
		sll2.addNode(6);
		sll2.addNode(5);
		sll2.addNode(4);
		sll2.addNode(3);
		sll2.addNode(2);
		sll2.addNode(1);
		// Test A
		Console.WriteLine(" Before folding");
		sll1.display();
		// Form of folding
		//      1 → 2 → 3 → 4 ──┐
		// NULL ← 8 ← 7 ← 6 ← 5⤶
		sll1.foldList();
		// After merging
		// 1 → 8 → 2 → 7 → 3 → 6 → 4 → 5 → NULL
		Console.WriteLine(" After folding");
		sll1.display();
		// Test B
		Console.WriteLine(" Before folding");
		sll2.display();
		// Form of folding
		//      1 → 2 → 3 → 4 
		// NULL ← 7 ← 6 ← 5⤶
		sll2.foldList();
		// After merging
		// 1 → 7 → 2 → 6 → 3 → 5 → 4 → NULL
		Console.WriteLine(" After folding");
		sll2.display();
	}
}

Output

 Before folding
 1 → 2 → 3 → 4 → 5 → 6 → 7 → 8 → NULL
 After folding
 1 → 8 → 2 → 7 → 3 → 6 → 4 → 5 → NULL
 Before folding
 1 → 2 → 3 → 4 → 5 → 6 → 7 → NULL
 After folding
 1 → 7 → 2 → 6 → 3 → 5 → 4 → NULL