greedy algorithm for graph coloring

// A Java program to implement greedy algorithm for graph coloring
import java.io.*;
import java.util.*;
import java.util.LinkedList;

// This class represents an undirected graph using adjacency list
class Graph
{
	private int V; // No. of vertices
	private LinkedList<Integer> adj[]; //Adjacency List

	//Constructor
	Graph(int v)
	{
		V = v;
		adj = new LinkedList[v];
		for (int i=0; i<v; ++i)
			adj[i] = new LinkedList();
	}

	//Function to add an edge into the graph
	void addEdge(int v,int w)
	{
		adj[v].add(w);
		adj[w].add(v); //Graph is undirected
	}

	// Assigns colors (starting from 0) to all vertices and
	// prints the assignment of colors
	void greedyColoring()
	{
		int result[] = new int[V];

		// Initialize all vertices as unassigned
		Arrays.fill(result, -1);

		// Assign the first color to first vertex
		result[0] = 0;

		// A temporary array to store the available colors. False
		// value of available[cr] would mean that the color cr is
		// assigned to one of its adjacent vertices
		boolean available[] = new boolean[V];
		
		// Initially, all colors are available
		Arrays.fill(available, true);

		// Assign colors to remaining V-1 vertices
		for (int u = 1; u < V; u++)
		{
			// Process all adjacent vertices and flag their colors
			// as unavailable
			Iterator<Integer> it = adj[u].iterator() ;
			while (it.hasNext())
			{
				int i = it.next();
				if (result[i] != -1)
					available[result[i]] = false;
			}

			// Find the first available color
			int cr;
			for (cr = 0; cr < V; cr++){
				if (available[cr])
					break;
			}

			result[u] = cr; // Assign the found color

			// Reset the values back to true for the next iteration
			Arrays.fill(available, true);
		}

		// print the result
		for (int u = 0; u < V; u++)
			System.out.println("Vertex " + u + " ---> Color "
								+ result[u]);
	}

	// Driver method
	public static void main(String args[])
	{
		Graph g1 = new Graph(5);
		g1.addEdge(0, 1);
		g1.addEdge(0, 2);
		g1.addEdge(1, 2);
		g1.addEdge(1, 3);
		g1.addEdge(2, 3);
		g1.addEdge(3, 4);
		System.out.println("Coloring of graph 1");
		g1.greedyColoring();

		System.out.println();
		Graph g2 = new Graph(5);
		g2.addEdge(0, 1);
		g2.addEdge(0, 2);
		g2.addEdge(1, 2);
		g2.addEdge(1, 4);
		g2.addEdge(2, 4);
		g2.addEdge(4, 3);
		System.out.println("Coloring of graph 2 ");
		g2.greedyColoring();
	}
}
// This code is contributed by Aakash Hasija