How to implement MINIMAX algorithm for Checkers Game in Java?

Here's the code so far, required to add Minimax algorithm (function) below, just before the main class. I was trying to understand this pseudocode, so I can apply to my case. Unfortunately, I couldn't really understand.

function minimax(node, depth, maximizingPlayer) is
if depth = 0 or node is a terminal node then
return the heuristic value of node
if maximizingPlayer then
value := −∞
for each child of node do
value := max(value, minimax(child, depth − 1, FALSE))
return value
else (* minimizing player *)
value := +∞
for each child of node do
value := min(value, minimax(child, depth − 1, TRUE))
return value
import java.awt.*;
import javax.swing.*;
import java.applet.*;
import java.net.*;

public class Checkers extends JFrame {

    private static int [][] boardPlan = {
        {0, 0, 0, 0, 0, 0, 0, 0},   //*** blue pieces become king here
        {0, 0, 0, 0, 0, 0, 0, 0},
        {0, 0, 0, 0, 0, 0, 0, 0},
        {0, 0, 0, 0, 0, 0, 0, 0},
        {0, 0, 0, 0, 0, 0, 0, 1},
        {1, 0, 4, 0, 3, 0, 0, 0},
        {0, 0, 0, 0, 0, 0, 0, 0},
        {0, 0, 0, 0, 2, 0, 0, 0}    //*** red pieces become king here
    };

    //*** the legend strings
    private String[] legend = {"blank", "bs", "bk", "rs", "rk" };

    //*** create the checkers board
    private GameBoard board;

    //*** the xy dimensions of each checkers cell on board
    private int cellDimension;

    //*** pause in seconds inbetween moves
    private static int pauseDuration = 500;

    Checkers() {
        //*** set up the initial configuration of the board
        board = new GameBoard(boardPlan);

        //*** each board cell is 70 pixels long and wide
        cellDimension = 70;

        //*** set up the frame containign the board
        getContentPane().setLayout(new GridLayout());
        setSize(boardPlan.length * cellDimension, boardPlan.length * cellDimension);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        getContentPane().add(board);

        //*** enable viewer
        setVisible(true);

        //*** place all initial pieces on board and pause a bit
        putInitialPieces();
        pause(2 * pauseDuration);
    }

    public void pause(int milliseconds) {
        try
        {Thread.sleep(milliseconds);}

        catch (Exception e)
        {}
    }

    void putPiece(int i, int j, String piece) {
        //*** can do error checking here to make sure pieces are bs, bk, rs, rk
        board.drawPiece(i, j, "images/" + piece + ".jpg");
    }

    void putInitialPieces() {
        //*** use legend variables to draw one piece at a time
        for (int i = 0; i < boardPlan.length; i++)
            for (int j = 0; j < boardPlan.length; j++)
                if (boardPlan[i][j] != 0)
                { board.drawPiece(i, j, "images/" + legend[boardPlan[i][j]] + ".jpg"); }
    }

    boolean legalPosition(int i) {
        //*** can't go outside board boundaries
        return ((i >= 0) && (i < boardPlan.length));
    }

    void movePiece(int i1, int j1, int i2, int j2, String piece) {
        //*** raise exception if outside the board or moving into a non-empty
        //*** cell
        if ((boardPlan[i2][j2] != 0) || !legalPosition(i1) || !legalPosition(i2)
                || !legalPosition(j1) || !legalPosition(j1))
        { throw new IllegalMoveException("An illegal move was attempted."); }

        //*** informative console messages
        System.out.println("Moved " + piece + " from position [" +
                           i1 + ", " + j1 + "] to [" + i2 + ", " + j2 + "]");

        //*** erase the old cell
        board.drawPiece(i1, j1, "images/blank.jpg");

        //*** draw the new cell
        board.drawPiece(i2, j2, "images/" + piece + ".jpg");

        //*** erase any captured piece from the board
        if ((Math.abs(i1 - i2) == 2) && (Math.abs(j1 - j2) == 2)) {
            //*** this handles  hops of length 2
            //*** the captured piece is halfway in between the two moves
            int captured_i = i1 + (i2 - i1) / 2;
            int captured_j = j1 + (j2 - j1) / 2;

            //*** now wait a bit
            pause(pauseDuration);

            //*** erase the captured cell
            board.drawPiece(captured_i, captured_j, "images/blank.jpg");

            //*** print which piece was captured
            System.out.println("Captured " + legend[boardPlan[captured_i][captured_j]] +
                               " from position [" + captured_i + ", " + captured_j + "]");

            //*** the captured piece is removed from the board with a bang
            boardPlan[captured_i][captured_j] = 0;
            Applet.newAudioClip(getClass().getResource("images/hit.wav")).play();
        }

        //*** update the internal representation of the board by moving the old
        //*** piece into its new position and leaving a blank in its old position
        boardPlan[i2][j2] = boardPlan[i1][j1];
        boardPlan[i1][j1] = 0;

        //*** red single is kinged
        if ( (i2 == boardPlan.length - 1) && (boardPlan[i2][j2] == 3) ) {
            boardPlan[i2][j2] = 4;
            putPiece(i2, j2, "rk");
        }

        //*** blue single is kinged
        if ( (i2 == 0) && (boardPlan[i2][j2] == 1) ) {
            boardPlan[i2][j2] = 2;
            putPiece(i2, j2, "bk");
        }

        //*** now wait a bit
        pause(pauseDuration);
    }

    //*** incorporate your MINIMAX algorithm in here
    //***********************************************************************
    public static void main(String [] args) {
        //*** create a new game and make it visible
        Checkers game = new Checkers();


        //*** arbitrarily move a few pieces around
        //while (!game.done())
        {
            try {
                //*** move a bs piece from board[4][7] to board[3][6]
                game.movePiece(4, 7, 3, 6, "bs");

                //*** move the rk from board[5][2] to board[4][1]
                game.movePiece(5, 2, 4, 1, "rk");

                //*** move a bs piece from board[5][0] to board[3][2]
                //*** must capture rk in position board[4][1]
                game.movePiece(5, 0, 3, 2, "bs");

                //*** move the bk from board[7][4] to board[6]1]
                game.movePiece(7, 4, 6, 3, "bk");

                //*** move the rs from board[5][4] to board[7][2]
                game.movePiece(5, 4, 7, 2, "rs");

                //*** a few more moves just for fun
                game.movePiece(3, 2, 2, 3, "bs");
                game.movePiece(2, 3, 1, 4, "bs");
                game.movePiece(1, 4, 0, 5, "bs");
                game.movePiece(3, 6, 2, 5, "bs");
                game.movePiece(2, 5, 1, 4, "bs");
                game.movePiece(1, 4, 0, 3, "bs");

            } catch (IllegalMoveException e)
            {e.printStackTrace();}
        }
    }
}

I've been trying for few days to search for the solution, but couldn't find the right one that associate with the code above. I would appreciate for your time and solution. Thanks!



Read more here: https://stackoverflow.com/questions/64398538/how-to-implement-minimax-algorithm-for-checkers-game-in-java

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