Find indegree and outdegree of a directed graph in kotlin

Kotlin program for Find indegree and outdegree of a directed graph. Here problem description and explanation.

/*
    Kotlin Program for 
    Show degree of vertex in directed graph
*/
class AjlistNode
{
	// Vertices node key
	var id: Int;
	var next: AjlistNode ? ;
	constructor(id: Int)
	{
		// Set value of node key
		this.id = id;
		this.next = null;
	}
}
class Vertices
{
	var data: Int;
	var next: AjlistNode ? ;
	var last: AjlistNode ? ;
	constructor(data: Int)
	{
		this.data = data;
		this.next = null;
		this.last = null;
	}
}
class Graph
{
	// Number of Vertices
	var size: Int;
	var node: Array < Vertices ? > ;
	constructor(size: Int)
	{
		// Set value
		this.size = size;
		this.node = Array(size)
		{
			null
		};
		this.setData();
	}
	// Set initial node value
	fun setData(): Unit
	{
		if (this.size <= 0)
		{
			println("\nEmpty Graph");
		}
		else
		{
			var index: Int = 0;
			while (index < this.size)
			{
				// Set initial node value
				this.node[index] = Vertices(index);
				index += 1;
			}
		}
	}
	//  Handling the request of adding new edge
	fun addEdge(start: Int, last: Int): Unit
	{
		if (start >= 0 && start < this.size && 
            last >= 0 && last < this.size)
		{
			// Safe connection
			val edge: AjlistNode = AjlistNode(last);
			if (this.node[start]?.next == null)
			{
				this.node[start]?.next = edge;
			}
			else
			{
				// Add edge at the end
				this.node[start]?.last?.next = edge;
			}
			// Get last edge 
			this.node[start]?.last = edge;
		}
		else
		{
			// When invalid nodes
			println("\nHere Something Wrong");
		}
	}
	fun printGraph(): Unit
	{
		if (this.size > 0)
		{
			var index: Int = 0;
			// Print graph ajlist Node value
			while (index < this.size)
			{
				print("\nAdjacency list of vertex " + index + " : ");
				var temp: AjlistNode ? = this.node[index]?.next;
				while (temp != null)
				{
					// Display graph node 
					print(" " + this.node[temp.id]?.data);
					// Visit to next edge
					temp = temp.next;
				}
				index += 1;
			}
		}
	}
	// Find indegree and outdegree of 
	// each nodes of a given graph
	fun findDegree(indegree: Array < Int > , 
                   outdegree: Array < Int > ): Unit
	{
		var temp: AjlistNode ? ;
		var length: Int = 0;
		var i: Int = 0;
		while (i < this.size)
		{
			temp = this.node[i]?.next;
			
			while (temp != null)
			{
				// Update indegree
				indegree[temp.id] += 1;
				temp = temp.next;
				length += 1;
			}
			// Set outdegree value
			outdegree[i] = length;
			i += 1;
           length = 0;
		}
	}
	fun showDegree(): Unit
	{
		if (this.size > 0)
		{
			val indegree: Array < Int > = Array(this.size)
			{
				0
			};
			val outdegree: Array < Int > = Array(this.size)
			{
				0
			};
		
			// Find degree
			this.findDegree(indegree, outdegree);
			println("\n");
			var i: Int = 0;
			// Display result
			while (i < this.size)
			{
				println("Node [" + i + "] indegree [" + 
                        indegree[i] + "] outdegree [" + 
                        outdegree[i] + "]");
				i += 1;
			}
		}
		else
		{
			print("Empty Graph");
		}
	}
}
fun main(args: Array < String > ): Unit
{
	// 6 implies the number of nodes in graph
	val g: Graph = Graph(6);
	// Connected two node with Edges
	g.addEdge(0, 1);
	g.addEdge(0, 2);
	g.addEdge(0, 5);
	g.addEdge(2, 3);
	g.addEdge(3, 1);
	g.addEdge(4, 0);
	g.addEdge(4, 1);
	g.addEdge(5, 0);
	g.addEdge(5, 2);
	g.printGraph();
	// Test
	g.showDegree();
}

Output

Adjacency list of vertex 0 :  1 2 5
Adjacency list of vertex 1 :
Adjacency list of vertex 2 :  3
Adjacency list of vertex 3 :  1
Adjacency list of vertex 4 :  0 1
Adjacency list of vertex 5 :  0 2

Node [0] indegree [2] outdegree [3]
Node [1] indegree [3] outdegree [0]
Node [2] indegree [2] outdegree [1]
Node [3] indegree [1] outdegree [1]
Node [4] indegree [0] outdegree [2]
Node [5] indegree [1] outdegree [2]