construct a linked list from 2d matrix in swift

Swift program for construct a linked list from 2d matrix. Here problem description and other solutions.

import Foundation
// Swift 4 program for
// Construct a linked list from 2D matrix
class LinkNode
{
	var data: Int;
	var next: LinkNode? ;
	var down: LinkNode? ;
	init(_ data: Int)
	{
		self.data = data;
		self.next = nil;
		self.down = nil;
	}
}
class DoublyLinkedList
{
	var head: LinkNode? ;
	init()
	{
		self.head = nil;
	}
	func display()
	{
		if (self.head == nil)
		{
			print("Empty linked list", terminator: "");
		}
		else
		{
			var front: LinkNode? = self.head;
			var right: LinkNode? = nil;
			while (front  != nil)
			{
				right = front;
				while (right  != nil)
				{
					print(right!.data, terminator:  "  ");
					right = right!.next;
				}
				print();
				// Visit to down node
				front = front!.down;
			}
		}
	}
	func insertData(_ matrix: [
		[Int]
	], _ rows: Int, _ cols: Int)
	{
		// Some auxiliary variables
		var levelHead: LinkNode? = nil;
		var root: LinkNode? = nil;
		var perv: LinkNode? = nil;
		var i: Int = 0;
		var j: Int = 0;
		// Add first row elements into result list 
		while (i < cols)
		{
			if (self.head == nil)
			{
				// Add first node
				self.head = LinkNode(matrix[0][i]);
				levelHead = self.head;
			}
			else
			{
				// next head
				levelHead!.next = LinkNode(matrix[0][i]);
				levelHead = levelHead!.next;
			}
			i += 1;
		}
		// Get first element    
		levelHead = self.head;
		i = 1;
		// Add all the bottom element of each column
		while (i < rows)
		{
			root = nil;
			perv = root;
			while (j < cols)
			{
				levelHead!.down = LinkNode(matrix[i][j]);
				if (root == nil)
				{
					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;
		}
	}
	static func main(_ args: [String])
	{
		let dll: DoublyLinkedList = DoublyLinkedList();
		// Create 2D metrix
		let matrix: [
			[Int]
		] = [
			[1, 6, 9, 2, -9],
			[2, 5, -5, 7, 1],
			[3, 4, 1, 8, 2]
		];
		let rows: Int = matrix.count;
		let cols: Int = matrix[0].count;
		dll.insertData(matrix, rows, cols);
		dll.display();
	}
}
DoublyLinkedList.main([String]());

Output

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