Arrange consonants and vowels nodes in a linked list in kotlin

Kotlin program for Arrange consonants and vowels nodes in a linked list. Here more information.

/*
  Kotlin program for 
  Arrange consonants and vowels nodes in a linked list
*/
// Linked list node
class LinkNode
{
	var data: Char;
	var next: LinkNode ? ;
	constructor(data: Char)
	{
		this.data = data;
		this.next = null;
	}
}
class SingleLL
{
	var head: LinkNode ? ;
	var tail: LinkNode ? ;
	constructor()
	{
		this.head = null;
		this.tail = null;
	}
	// Add new Node at end of linked list 
	fun appendNode(node: LinkNode ? ): Unit
	{
		if (this.head == null)
		{
			this.head = node;
		}
		else
		{
			// Append the node at last position
			this.tail?.next = node;
		}
		this.tail = node;
	}
	// Handles the request of adding new node in linked list
	fun addNode(data: Char): Unit
	{
		val node: LinkNode = LinkNode(data);
		this.appendNode(node);
	}
	// Display linked list element
	fun display(): Unit
	{
		if (this.head == null)
		{
			println("\n Empty linked list");
			return;
		}
		var temp: LinkNode ? = this.head;
		// iterating linked list elements
		while (temp != null)
		{
			print(" " + temp.data + " →");
			// Visit to next node
			temp = temp.next;
		}
		print(" NULL\n");
	}
	// Determine that given value is an vowel or not
	fun isVowels(value: Char): Boolean
	{
		if (value == 'a' || value == 'e' || 
            value == 'i' || value == 'o' || 
            value == 'u' || value == 'A' || 
            value == 'E' || value == 'I' || 
            value == 'O' || value == 'U')
		{
			return true;
		}
		return false;
	}
	// Arrange the nodes in front position of vowels 
	// and end with consonants
	fun arrangeNodes(): Unit
	{
		if (this.head == null)
		{
			println("\n Empty linked list");
			return;
		}
		// Define some auxiliary variable
		val vowel: SingleLL = SingleLL();
		val consonant: SingleLL = SingleLL();
		var auxiliary: LinkNode ? = this.head;
		var ordinary: LinkNode ? ;
		// iterate linked list nodes
		while (auxiliary != null)
		{
			ordinary = auxiliary;
			auxiliary = auxiliary.next;
			if (this.isVowels(ordinary.data) == true)
			{
				// Add node into volwel list
				vowel.appendNode(ordinary);
			}
			else
			{
				consonant.appendNode(ordinary);
			}
			ordinary.next = null;
		}
		if (vowel.head != null)
		{
			// Set new head node of resultant linked list
			this.head = vowel.head;
			// Connect vowel and consonant linked list
			vowel.tail?.next = consonant.head;
			if (consonant.tail != null)
			{
				// When consonant node exists
				// Set new tail node of resultant linked list 
				this.tail = consonant.tail;
			}
			else
			{
				// When consonant nodes not exists
				this.tail = vowel.tail;
			}
		}
		else
		{
			// When vowels not exist
			this.head = consonant.head;
			this.tail = consonant.tail;
		}
	}
}
fun main(args: Array < String > ): Unit
{
	val sll: SingleLL = SingleLL();
	// Constructed linked list
	sll.addNode('R');
	sll.addNode('E');
	sll.addNode('G');
	sll.addNode('U');
	sll.addNode('L');
	sll.addNode('A');
	sll.addNode('T');
	sll.addNode('I');
	sll.addNode('O');
	sll.addNode('N');
	println(" Before Arrange");
	// R → E → G → U → L → A → T → I → O → N → NULL
	sll.display();
	sll.arrangeNodes();
	println(" After Arrange");
	// E → U → A → I → O → R → G → L → T → N → NULL
	sll.display();
}

Output

 Before Arrange
 R → E → G → U → L → A → T → I → O → N → NULL
 After Arrange
 E → U → A → I → O → R → G → L → T → N → NULL