construct a linked list from 2d matrix in c++

C++ program for construct a linked list from 2d matrix. Here problem description and explanation.

// Include header file
#include <iostream>
#include <vector>

using namespace std;
// C++ program for
// Construct a linked list from 2D matrix
class LinkNode
{
	public: int data;
	LinkNode *next;
	LinkNode *down;
	LinkNode(int data)
	{
		this->data = data;
		this->next = nullptr;
		this->down = nullptr;
	}
};
class DoublyLinkedList
{
	public: LinkNode *head;
	DoublyLinkedList()
	{
		this->head = nullptr;
	}
	void display()
	{
		if (this->head == nullptr)
		{
			cout << "Empty linked list";
		}
		else
		{
			LinkNode *front = this->head;
			LinkNode *right = nullptr;
			while (front != nullptr)
			{
				right = front;
				while (right != nullptr)
				{
					cout << right->data << "  ";
					right = right->next;
				}
				cout << "\n";
				// Visit to down node
				front = front->down;
			}
		}
	}
	void insertData(vector < vector < int >> matrix, 
                    int rows, int cols)
	{
		// Some auxiliary variables
		LinkNode *levelHead = nullptr;
		LinkNode *root = nullptr;
		LinkNode *perv = nullptr;
		int i = 0;
		int j = 0;
		// Add first row elements into result list 
		while (i < cols)
		{
			if (this->head == nullptr)
			{
				// Add first node
				this->head = new LinkNode(matrix[0][i]);
				levelHead = this->head;
			}
			else
			{
				// next head
				levelHead->next = new LinkNode(matrix[0][i]);
				levelHead = levelHead->next;
			}
			i++;
		}
		// Get first element    
		levelHead = this->head;
		i = 1;
		// Add all the bottom element of each column
		while (i < rows)
		{
			root = nullptr;
			perv = root;
			while (j < cols)
			{
				levelHead->down = new LinkNode(matrix[i][j]);
				if (root == nullptr)
				{
					root = levelHead->down;
					perv = root;
				}
				else
				{
					perv->next = levelHead->down;
					perv = levelHead->down;
				}
				levelHead = levelHead->next;
				j++;
			}
			levelHead = root;
			// reset col
			j = 0;
			// change row
			i++;
		}
	}
};
int main()
{
	DoublyLinkedList *dll = new DoublyLinkedList();
	// Create 2D metrix
	vector < vector < int >> matrix {
		{
			1 , 6 , 9 , 2 , -9
		} , {
			2 , 5 , -5 , 7 , 1
		} , {
			3 , 4 , 1 , 8 , 2
		}
	};
	int rows = matrix.size();
	int cols = matrix[0].size();
	dll->insertData(matrix, rows, cols);
	dll->display();
	return 0;
}

Output

1  6  9  2  -9
2  5  -5  7  1
3  4  1  8  2