Find largest node value of doubly linked list in swift

Swift program for Find largest node value of doubly linked list. Here problem description and other solutions.

import Foundation
// Swift 4 program for
// Find max value in doubly linked list

// Define class of linked list Node
class LinkNode
{
	var data: Int;
	var next: LinkNode? ;
	var prev: LinkNode? ;
	init(_ data: Int)
	{
		self.data = data;
		self.next = nil;
		self.prev = nil;
	}
}
class DoublyLinkedList
{
	var head: LinkNode? ;
	var tail: LinkNode? ;
	init()
	{
		self.head = nil;
		self.tail = nil;
	}
	// Insert new node at end position
	func insert(_ value: Int)
	{
		// Create a new node
		let node: LinkNode? = LinkNode(value);
		if (self.head == nil)
		{
			// Add first node
			self.head = node;
			self.tail = node;
			return;
		}
		// Add node at last position
		self.tail!.next = node;
		node!.prev = self.tail;
		self.tail = node;
	}
	func maximum() -> Int
	{
		if (self.head == nil)
		{
			// When empty linked list
			return 0;
		}
		var result: Int = self.head!.data;
		// Get first node of linked list
		var temp: LinkNode? = self.head;
		// iterate linked list 
		while (temp  != nil)
		{
			if (temp!.data > result)
			{
				result = temp!.data;
			}
			// Visit to next node
			temp = temp!.next;
		}
		// Return maximum value
		return result;
	}
	static func main(_ args: [String])
	{
		let dll: DoublyLinkedList? = DoublyLinkedList();
		// Insert following linked list nodes
		dll!.insert(14);
		dll!.insert(31);
		dll!.insert(12);
		dll!.insert(15);
		dll!.insert(11);
		dll!.insert(25);
		print("Maximum  :",dll!.maximum());
	}
}
DoublyLinkedList.main([String]());

Output

Maximum  : 31