# Adjacency list representation of directed graph in scala

Scala program for Adjacency list representation of directed graph. Here problem description and explanation.

```
/*
Scala Program for
Directed graph representation using adjacency list
*/
class AjlistNode(
// Vertices node key
var id: Int,
var next: AjlistNode)
{
def this(id: Int)
{
// Set value of node key
this(id, null);
}
}
class Vertices(var data: Int,
var next: AjlistNode,
var last: AjlistNode)
{
def this(data: Int)
{
this(data, null, null);
}
}
class Graph(
// Number of Vertices
var size: Int,
var node: Array[Vertices])
{
def this(size: Int)
{
// Set value
this(size, Array.fill[Vertices](size)(null));
this.setData();
}
// Set initial node value
def setData(): Unit = {
if (size <= 0)
{
println("\nEmpty Graph");
}
else
{
var index: Int = 0;
while (index < size)
{
// Set initial node value
node(index) = new Vertices(index);
index += 1;
}
}
}
// Connect two nodes
def connect(start: Int, last: Int): Unit = {
var edge: AjlistNode = new AjlistNode(last);
if (node(start).next == null)
{
node(start).next = edge;
}
else
{
// Add edge at the end
node(start).last.next = edge;
}
// Get last edge
node(start).last = edge;
}
// Handling the request of adding new edge
def addEdge(start: Int, last: Int): Unit = {
if (start >= 0 && start < size && last >= 0 && last < size)
{
// Safe connection
connect(start, last);
}
else
{
// When invalid nodes
println("\nHere Something Wrong");
}
}
def printGraph(): Unit = {
if (size > 0)
{
var index: Int = 0;
// Print graph ajlist Node value
while (index < size)
{
print("\nAdjacency list of vertex " + index + " :");
var temp: AjlistNode = node(index).next;
while (temp != null)
{
// Display graph node
print(" " + node(temp.id).data);
// visit to next edge
temp = temp.next;
}
index += 1;
}
}
}
}
object Main
{
def main(args: Array[String]): Unit = {
// 5 implies the number of nodes in graph
var g: Graph = new Graph(5);
// Connect node with an edge
g.addEdge(0, 1);
g.addEdge(1, 2);
g.addEdge(1, 4);
g.addEdge(2, 0);
g.addEdge(2, 3);
g.addEdge(4, 3);
// print graph element
g.printGraph();
}
}
```

**Output**

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

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