Find second last element of linked list in swift

Swift program for Find second last element of linked list. Here more information.

import Foundation
// Swift 4 program for
// Find the second last node of a linked list

// Node of Linked List
class LinkNode
{
	var data: Int;
	var next: LinkNode? ;
	init(_ data: Int)
	{
		// Set node value
		self.data = data;
		self.next = nil;
	}
}
class SingleLL
{
	var head: LinkNode? ;
	var tail: LinkNode? ;
	init()
	{
		self.head = nil;
		self.tail = nil;
	}
	// Add new node at the end of linked list
	func insert(_ value: Int)
	{
		// Create a new node
		let node: LinkNode? = LinkNode(value);
		if (self.head == nil)
		{
			self.head = node;
		}
		else
		{
			self.tail!.next = node;
		}
		self.tail = node;
	}
	// Display linked list element
	func display()
	{
		if (self.head == nil)
		{
			return;
		}
		var temp: LinkNode? = self.head;
		// iterating linked list elements
		while (temp  != nil)
		{
			print(String(temp!.data) + " → ", terminator: "");
			// Visit to next node
			temp = temp!.next;
		}
		print("null");
	}
	//Find the second last node of a linked list
	func secondLast()
	{
		var node: LinkNode? = self.head;
		if (node == nil)
		{
			print("Empty linked list");
		}
		else if (node!.next == nil)
		{
			print("Only one node in this linked list\n");
		}
		else
		{
			// Find second last node
			while (node!.next  != nil && 
                   node!.next!.next  != nil)
			{
				// Visit to second next node
				node = node!.next!.next;
			}
			print("Second last element is : ",node!.data);
		}
	}
	static func main(_ args: [String])
	{
		let sll: SingleLL? = SingleLL();
		// Add linked list node
		sll!.insert(6);
		sll!.insert(3);
		sll!.insert(2);
		sll!.insert(7);
		sll!.insert(1);
		sll!.insert(9);
		print("Linked List");
		// 6 → 3 → 2 → 7 → 1 → 9 → null
		sll!.display();
		sll!.secondLast();
	}
}
SingleLL.main([String]());

Output

Linked List
6 → 3 → 2 → 7 → 1 → 9 → null
Second last element is :  1