programming-examples/java/Hard_Graph_Problems/Java Program to Check whether Graph is a Bipartite using 2 Color Algorithm.java

/*This Java program is to Check whether Graph is a Bipartite using 2 Color Algorithm.In the mathematical field of graph theory, a bipartite graph (or bigraph) is a graph whose vertices can be divided into two disjoint sets and such that every edge connects a vertex in to one in ; that is, and are each independent sets.
The two sets and may be thought of as a coloring of the graph with two colors: if one colors all nodes in blue, and all nodes in green, each edge has endpoints of differing colors, as is required in the graph coloring problem.In contrast, such a coloring is impossible in the case of a non-bipartite graph, such as a triangle.*/

import java.util.InputMismatchException;
import java.util.Scanner;
public class CheckBipartite
{
    private int numberOfNodes;
    private static final int NO_OF_COLOR = 2;

    private boolean isSafe(int vertex,int[][] adjacencyMatrix, int [] colored, int color)
    {
        for (int destination = 1; destination <= numberOfNodes; destination++)
            {
                if (adjacencyMatrix[vertex][destination] == 1 && colored[destination] == color)
                    {
                        return false;
                    }
            }
        return true;
    }

    private boolean checkBipartiteUtil(int adjacencyMatrix[][], int[] colored, int vertex)
    {
        if (vertex > numberOfNodes)
            {
                return true;
            }
        for (int colorNum = 1; colorNum <= NO_OF_COLOR; colorNum++)
            {
                if (isSafe(vertex, adjacencyMatrix, colored, colorNum))
                    {
                        colored[vertex] = colorNum;
                        if (checkBipartiteUtil(adjacencyMatrix, colored, vertex + 1))
                            {
                                return true;
                            }
                        else
                            {
                                return false;
                            }
                    }
            }
        return false;
    }

    public boolean checkBipartite(int adjacencyMatrix[][])
    {
        boolean bipartite = true;
        numberOfNodes = adjacencyMatrix[1].length - 1;
        int[] colored = new int[numberOfNodes + 1];
        for (int vertex = 1; vertex <= numberOfNodes; vertex++)
            {
                colored[vertex] = 0;
            }
        if (!checkBipartiteUtil(adjacencyMatrix, colored, 1))
            {
                bipartite = false;
            }
        return bipartite;
    }

    public static void main(String... arg)
    {
        int number_of_nodes;
        Scanner scanner = null;
        try
            {
                System.out.println("Enter the number of nodes in the graph");
                scanner = new Scanner(System.in);
                number_of_nodes = scanner.nextInt();
                int adjacency_matrix[][] = new int[number_of_nodes + 1][number_of_nodes + 1];
                System.out.println("Enter the adjacency matrix");
                for (int i = 1; i <= number_of_nodes; i++)
                    {
                        for (int j = 1; j <= number_of_nodes; j++)
                            {
                                adjacency_matrix[i][j] = scanner.nextInt();
                            }
                    }
                for (int i = 1; i <= number_of_nodes; i++)
                    {
                        for (int j = 1; j <= number_of_nodes; j++)
                            {
                                if (adjacency_matrix[i][j] == 1 && adjacency_matrix[j][i] == 0)
                                    {
                                        adjacency_matrix[j][i] = 1;
                                    }
                            }
                    }
                CheckBipartite bipartite = new CheckBipartite();
                if (bipartite.checkBipartite(adjacency_matrix))
                    {
                        System.out.println("the given graph is bipartite");
                    }
                else
                    {
                        System.out.println("the given graph is not bipartite");
                    }
            }
        catch (InputMismatchException inputMismatch)
            {
                System.out.println("Wrong Input format");
            }
        scanner.close();
    }
}

/*
Enter the number of nodes in the graph
6
Enter the adjacency matrix
0 1 0 1 0 1
1 0 1 0 1 0
0 1 0 1 0 1
1 0 1 0 1 0
0 1 0 1 0 1
1 0 1 0 1 0
the given graph is bipartite