Flatten a folded linked list in c++

C++ program for Flatten a folded linked list. Here problem description and explanation.

// Include header file
#include <iostream>
using namespace std;
/*
  C++ program for
  Unfold a folded linked list OR
  flatten folded linked list
*/
// Linked list node
class LinkNode
{
	public: int data;
	LinkNode *next;
	LinkNode(int data)
	{
		this->data = data;
		this->next = nullptr;
	}
};
class SingleLL
{
	public: LinkNode *head;
	SingleLL()
	{
		this->head = nullptr;
	}
	// Insert node at the beginning of linked list
	void addNode(int data)
	{
		// Create node
		LinkNode *node = new LinkNode(data);
		node->next = this->head;
		// Set new head
		this->head = node;
	}
	// Display linked list element
	void display()
	{
		if (this->head == nullptr)
		{
			return;
		}
		LinkNode *temp = this->head;
		// iterating linked list elements
		while (temp != nullptr)
		{
			cout << " " << temp->data << " →";
			// Visit to next node
			temp = temp->next;
		}
		cout << " NULL" << endl;
	}
	// This is handle the request of unfold given linked list nodes
	void unfoldList()
	{
		if (this->head == nullptr)
		{
			cout << "\n Empty linked list" << endl;
			return;
		}
		LinkNode *temp = this->head;
		LinkNode *auxiliary = nullptr;
		LinkNode *hold = nullptr;
		// Loop which is separating the fold elements 
		while (temp->next != nullptr)
		{
			// Get the second element
			hold = temp->next;
			if (hold->next != nullptr)
			{
				// When exists pair of three elements
				temp->next = hold->next;
				// Visit to 3rd element
				temp = hold->next;
			}
			else
			{
				// When get last two elements
				temp->next = nullptr;
			}
			// Add new node at beginning of auxiliary linked list
			hold->next = auxiliary;
			// Make new head node
			auxiliary = hold;
		}
		if (temp != nullptr)
		{
			// Combine lists
			temp->next = auxiliary;
		}
	}
};
int main()
{
	// Create a empty linked lists
	SingleLL *sll1 = new SingleLL();
	SingleLL *sll2 = new SingleLL();
	//  Constructed first linked list
	//  2 → 5 → 1 → 8 → 10 → 4 → 9 → 7 → NULL
	sll1->addNode(7);
	sll1->addNode(9);
	sll1->addNode(4);
	sll1->addNode(10);
	sll1->addNode(8);
	sll1->addNode(1);
	sll1->addNode(5);
	sll1->addNode(2);
	// 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
	cout << " Before unfold" << endl;
	sll1->display();
	sll1->unfoldList();
	cout << " After unfold" << endl;
	sll1->display();
	// Test B
	cout << " Before unfold" << endl;
	sll2->display();
	sll2->unfoldList();
	cout << " After unfold" << endl;
	sll2->display();
	return 0;
}

Output

 Before unfold
 2 → 5 → 1 → 8 → 10 → 4 → 9 → 7 → NULL
 After unfold
 2 → 1 → 10 → 9 → 7 → 4 → 8 → 5 → NULL
 Before unfold
 1 → 2 → 3 → 4 → 5 → 6 → 7 → NULL
 After unfold
 1 → 3 → 5 → 7 → 6 → 4 → 2 → NULL