programming-examples/java/Graph_Problems_Algorithms/Java Program to Implement Graph Coloring Algorithm.java

/*This is a Java Program to Implement Graph Coloring Algorithm. Graph Coloring is a way of coloring the vertices of a undirected graph such that no two adjacent vertices share the same color.*/

/**
 **  Java Program to Implement Graph Coloring Algorithm
 **/

import java.util.Scanner;

/** Class GraphColoring **/
public class GraphColoring
{
    private int V, numOfColors;
    private int[] color;
    private int[][] graph;

    /** Function to assign color **/
    public void graphColor(int[][] g, int noc)
    {
        V = g.length;
        numOfColors = noc;
        color = new int[V];
        graph = g;
        try
            {
                solve(0);
                System.out.println("No solution");
            }
        catch (Exception e)
            {
                System.out.println("\nSolution exists ");
                display();
            }
    }
    /** function to assign colors recursively **/
    public void solve(int v) throws Exception
    {
        /** base case - solution found **/
        if (v == V)
            throw new Exception("Solution found");
        /** try all colours **/
        for (int c = 1; c <= numOfColors; c++)
            {
                if (isPossible(v, c))
                    {
                        /** assign and proceed with next vertex **/
                        color[v] = c;
                        solve(v + 1);
                        /** wrong assignement **/
                        color[v] = 0;
                    }
            }
    }
    /** function to check if it is valid to allot that color to vertex **/
    public boolean isPossible(int v, int c)
    {
        for (int i = 0; i < V; i++)
            if (graph[v][i] == 1 && c == color[i])
                return false;
        return true;
    }
    /** display solution **/
    public void display()
    {
        System.out.print("\nColors : ");
        for (int i = 0; i < V; i++)
            System.out.print(color[i] +" ");
        System.out.println();
    }
    /** Main function **/
    public static void main (String[] args)
    {
        Scanner scan = new Scanner(System.in);
        System.out.println("Graph Coloring Algorithm Test\n");
        /** Make an object of GraphColoring class **/
        GraphColoring gc = new GraphColoring();
        /** Accept number of vertices **/
        System.out.println("Enter number of verticesz\n");
        int V = scan.nextInt();
        /** get graph **/
        System.out.println("\nEnter matrix\n");
        int[][] graph = new int[V][V];
        for (int i = 0; i < V; i++)
            for (int j = 0; j < V; j++)
                graph[i][j] = scan.nextInt();
        System.out.println("\nEnter number of colors");
        int c = scan.nextInt();
        gc.graphColor(graph, c);
    }
}

/*
/**
 **  Java Program to Implement Graph Coloring Algorithm
 **/

import java.util.Scanner;

/** Class GraphColoring **/
public class GraphColoring
{
    private int V, numOfColors;
    private int[] color;
    private int[][] graph;

    /** Function to assign color **/
    public void graphColor(int[][] g, int noc)
    {
        V = g.length;
        numOfColors = noc;
        color = new int[V];
        graph = g;
        try
            {
                solve(0);
                System.out.println("No solution");
            }
        catch (Exception e)
            {
                System.out.println("\nSolution exists ");
                display();
            }
    }
    /** function to assign colors recursively **/
    public void solve(int v) throws Exception
    {
        /** base case - solution found **/
        if (v == V)
            throw new Exception("Solution found");
        /** try all colours **/
        for (int c = 1; c <= numOfColors; c++)
            {
                if (isPossible(v, c))
                    {
                        /** assign and proceed with next vertex **/
                        color[v] = c;
                        solve(v + 1);
                        /** wrong assignement **/
                        color[v] = 0;
                    }
            }
    }
    /** function to check if it is valid to allot that color to vertex **/
    public boolean isPossible(int v, int c)
    {
        for (int i = 0; i < V; i++)
            if (graph[v][i] == 1 && c == color[i])
                return false;
        return true;
    }
    /** display solution **/
    public void display()
    {
        System.out.print("\nColors : ");
        for (int i = 0; i < V; i++)
            System.out.print(color[i] +" ");
        System.out.println();
    }
    /** Main function **/
    public static void main (String[] args)
    {
        Scanner scan = new Scanner(System.in);
        System.out.println("Graph Coloring Algorithm Test\n");
        /** Make an object of GraphColoring class **/
        GraphColoring gc = new GraphColoring();
        /** Accept number of vertices **/
        System.out.println("Enter number of verticesz\n");
        int V = scan.nextInt();
        /** get graph **/
        System.out.println("\nEnter matrix\n");
        int[][] graph = new int[V][V];
        for (int i = 0; i < V; i++)
            for (int j = 0; j < V; j++)
                graph[i][j] = scan.nextInt();
        System.out.println("\nEnter number of colors");
        int c = scan.nextInt();
        gc.graphColor(graph, c);
    }
}