construct a linked list from 2d matrix in kotlin

Kotlin program for construct a linked list from 2d matrix. Here more information.

// Kotlin program for
// Construct a linked list from 2D matrix
class LinkNode
{
	var data: Int;
	var next: LinkNode ? ;
	var down: LinkNode ? ;
	constructor(data: Int)
	{
		this.data = data;
		this.next = null;
		this.down = null;
	}
}
class DoublyLinkedList
{
	var head: LinkNode ? ;
	constructor()
	{
		this.head = null;
	}
	fun display(): Unit
	{
		if (this.head == null)
		{
			print("Empty linked list");
		}
		else
		{
			var front: LinkNode ? = this.head;
			var right: LinkNode ? ;
			while (front != null)
			{
				right = front;
				while (right != null)
				{
					print("  " + right.data );
					right = right.next;
				}
				print("\n");
				// Visit to down node
				front = front.down;
			}
		}
	}
	fun insertData(matrix: Array < Array < Int >> , 
                   rows: Int, cols: Int): Unit
	{
		// Some auxiliary variables
		var levelHead: LinkNode ? = null;
		var root: LinkNode ? ;
		var perv: LinkNode ? ;
		var i: Int = 0;
		var j: Int = 0;
		// Add first row elements into result list 
		while (i < cols)
		{
			if (this.head == null)
			{
				// Add first node
				this.head = LinkNode(matrix[0][i]);
				levelHead = this.head;
			}
			else
			{
				// next head
				levelHead?.next = LinkNode(matrix[0][i]);
				levelHead = levelHead?.next;
			}
			i += 1;
		}
		// Get first element    
		levelHead = this.head;
		i = 1;
		// Add all the bottom element of each column
		while (i < rows)
		{
			root = null;
			perv = root;
			while (j < cols)
			{
				levelHead?.down = LinkNode(matrix[i][j]);
				if (root == null)
				{
					root = levelHead?.down;
					perv = root;
				}
				else
				{
					perv?.next = levelHead?.down;
					perv = levelHead?.down;
				}
				levelHead = levelHead?.next;
				j += 1;
			}
			levelHead = root;
			// reset col
			j = 0;
			// change row
			i += 1;
		}
	}
}
fun main(args: Array < String > ): Unit
{
	val dll: DoublyLinkedList = DoublyLinkedList();
	// Create 2D metrix
	val matrix: Array < Array < Int >> = arrayOf(
      arrayOf(1, 6, 9, 2, -9), 
      arrayOf(2, 5, -5, 7, 1), 
      arrayOf(3, 4, 1, 8, 2)
    );
	val rows: Int = matrix.count();
	val cols: Int = matrix[0].count();
	dll.insertData(matrix, rows, cols);
	dll.display();
}

Output

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