Simple NQueen Visualizer in JAVA to Visualize Backtracking.

NQueenBacktrackingVisualization.java

/**
 * Author:      Asif Ahmed
 * Site:        https://quickgrid.wordpress.com
 * Description: N Queen visualizer Sample.
 */

import javax.swing.*;
import java.awt.*;

/**
 * Created by computer science on 12/6/2015.
 */
public class NQueen {

    final static int M = 10;
    static JLabel [][] jLabel = new JLabel[M][M];


    static int board[][] = new int[M][M];


    static void printSolution(){

        for(int i = 0; i < M; ++i){
            for(int j = 0; j < M; ++j){
                System.out.printf("%d ", board[i][j]);
            }
            System.out.printf("\n");
        }

    }


    static boolean isSafe( int row, int col ) {

        try {
            Thread.sleep(10);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        for (int i = 0; i < col; ++i)
            if (board[row][i] == 1)
                return false;


        for (int i = row, j = col; i >= 0 && j >= 0; --i, --j) {

            if (board[i][j] == 1)
                return false;

        }

        for (int i = row, j = col; i < M && j >= 0; ++i, --j){

            if (board[i][j] == 1)
                return false;
        }

        return true;
    }



    static boolean findSolution( int col ){

        if(col >= M)
            return true;


        for( int i = 0; i < M; ++i ){

            //Increase the sleep value to slow down the animation
            try {
                Thread.sleep(0);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }

            if( isSafe( i, col) == true ){

                board[i][col] = 1;
                jLabel[i][col].setBackground(Color.ORANGE);


                if( findSolution( col + 1) == true )
                    return true;


                board[i][col] = 0;
                jLabel[i][col].setBackground(Color.WHITE);

                //jLabel[i][col].setBackground(Color.BLUE);


            }

        }


        return false;

    }

    static void solveNQueen(){



        try {
            Thread.sleep(500);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }


        // reset board
        for(int i = 0; i < M; ++i) {
            for (int j = 0; j < M; ++j) {

                try {
                    Thread.sleep(10);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }

                board[i][j] = 0;
                jLabel[i][j].setBackground(Color.BLUE);
            }
        }



        //If solution exist print otherwise show error message
        if( findSolution( 0 ) == false )
            System.out.println("No Solution.\n");
        else
            printSolution();

    }




    NQueen() {


        JFrame jFrame = new JFrame("NQueen Visualizer.");

        jFrame.setLayout(new GridLayout(M, M));
        jFrame.setSize(500, 500);

        jFrame.setDefaultCloseOperation(jFrame.EXIT_ON_CLOSE);


        for(int i = 0; i < M; ++i) {
            for (int j = 0; j < M; ++j) {
                jLabel[i][j] = new JLabel( "(" + i + "," + j + ")" );
                jLabel[i][j].setHorizontalAlignment(SwingConstants.CENTER);

                jLabel[i][j].setSize(50, 50);

                jLabel[i][j].setOpaque(true);

                //Random rand = new Random();
                //jLabel[i].setBackground(new Color(rand.nextFloat(), rand.nextFloat(), rand.nextFloat()));

                jFrame.add(jLabel[i][j]);
            }
        }


        jFrame.setVisible(true);

    }






    public static  void main( String args[] ){

        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                new NQueen();
            }
        });

        solveNQueen();

    }

}