Question

Hello, I am currently taking a Foundations of Programming course where we are learning the basics of Java.

I am struggling with a part of a question assigned by the professor.

He gave us this code to fill in:

import java.util.Arrays;
import java.util.Random;

public class RobotGo {

    public static Random r = new Random(58);

    public static void main(String[] args) {

        char[][] currentBoard = createRandomObstacle(createBoard(10, 20), 100);
        displayBoard(startNavigation(currentBoard))

    }

    public static int[] getRandomCoordinate(int maxY, int maxX) {
        int[] coor = new int[2];
        int y = r.nextInt(maxY);
        int x = r.nextInt(maxX);
        coor[0] = y;
        coor[1] = x;
        return coor;
    }
    public static char[][] createBoard(int row, int col) {
        if (row < 5 || col < 5) {
            throw new IllegalArgumentException("Both x and y axes must be greater than or equal to 5.");
        }
        char[][] board = new char[row][col];
        for (int i = 0; i < col; i++) {
            board[0][i] = '#';
        }
        for (int i = 1; i < row - 1; i++) {
            board[i][0] = '#';
            for (int j = 1; j < col - 1; j++) {
                board[i][j] = ' ';
            }
            board[i][col - 1] = '#';
        }
        for (int i = 0; i < col; i++) {
            board[row - 1][i] = '#';
        }
        board[1][1] = '.';
        board[row - 2][col - 2] = 'x';
        return board;
    }
    private static char[][] createRandomObstacle(char[][] board, int num) {
        int space = 0;

        for (int i = 0; i < board.length; i++) {
            for (int j = 0; j < board[i].length; j++) {
                if (board[i][j] == ' ') {
                    space += 1;
                }
            }
        }
        if (num > space) {
            throw new IllegalArgumentException("Too many obstacles");
        }
        for (int i = 0; i < num; i++) {
            int[] randCoord = getRandomCoordinate(board.length, board[0].length);
            while (board[randCoord[0]][randCoord[1]] != ' ') {
                randCoord = getRandomCoordinate(board.length, board[0].length);
            }
            board[randCoord[0]][randCoord[1]] = '#';
        }
        return board;
    }

    private static void displayBoard(char[][] board){
        for (int i = 0; i < board.length; i++) {
            for (int j = 0; j < board[i].length; j++) {
               if (board[i][j] != ' ') {
                    System.out.print(board[i][j]);
                }
            }
            System.out.println("");
        }
    }
}

The question is:

Write a method called startNavigation() that takes char[][] board and return the board char[][] which has all the moves labelled. For maze solving algorithm, you should use the right-hand rule solution. In this solution, the robot solves the maze by continuously following the right wall. In order to successfully implement the righthand rule solution, you might need to implement turnRight() and turnLeft() as your helper method.

For example, consider the following boards, char[][] board:

• board = [[#, #, #, #, #], [#, ., , , #], [#, , , , #], [#, , , x, #], [#, #, #, #, #]]; calling the startNavigation(board) should return: [[#, #, #, #, #], [#, ., , , #], [#, ., , , #], [#, ., ., x, #], [#, #, #, #, #]] and calling the displayBoard(board) should print:

#####

#. #

#. #

#..x#

#####

• board = [[#, #, #, #, #], [#, ., , , #], [#, , , #, #], [#, #, , x, #], [#, #, #, #, #]] calling the startNavigation(board) should return: [[#, #, #, #, #], [#, ., , , #], [#, ., ., #, #], [#, #, ., x, #], [#, #, #, #, #]] and calling the displayBoard(board) should print:

#####

#. #

#..##

##.x#

#####

Answer 1

Your examples are optimized they don't follow right hand rule, instead they use both right and left turn.

here is code that use right hand rule;

import java.util.Arrays;

import java.util.Random;

public class RobotGo {
    public static Random r = new Random(58);

    public static void main(String[] args) {
        char[][] currentBoard = createRandomObstacle(createBoard(10, 20), 0);
        displayBoard(startNavigation(currentBoard));
    }

    private static char[][] startNavigation(char[][] currentBoard) {
       boolean end = false;
       int posX = 1;
       int posY = 1;
       int dir = 1;//1 is down, 2 is right, 3 is up, 4 is left.
       long steps = 0;
       while(!end){
           switch (dir) {
           case 1:
               if(currentBoard[posX+1][posY]=='#'){
                   dir = turnRight(dir);
               }
               else{
                   posX++;
                   if(currentBoard[posX][posY]==' '){
                       currentBoard[posX][posY]='.';
                   }
                   steps++;
                   if(posX==(currentBoard.length-2) && posY==(currentBoard[0].length-2)){
                       end = true;
                   }
               }
               break;
           case 2:
               if(currentBoard[posX][posY+1]=='#'){
                   dir = turnRight(dir);
               }
               else{
                   posY++;
                   if(currentBoard[posX][posY]==' '){
                       currentBoard[posX][posY]='.';
                   }
                   steps++;
                   if(posX==(currentBoard.length-2) && posY==(currentBoard[0].length-2)){
                       end = true;
                   }
               }
               break;
           case 3:
               if(currentBoard[posX-1][posY]=='#'){
                   dir = turnRight(dir);
               }
               else{
                   posX--;
                   if(currentBoard[posX][posY]==' '){
                       currentBoard[posX][posY]='.';
                   }
                   steps++;
               }
               break;
           case 4:
               if(currentBoard[posX][posY-1]=='#'){
                   dir = turnRight(dir);
               }
               else{
                   posY--;
                   if(currentBoard[posX][posY]==' '){
                       currentBoard[posX][posY]='.';
                   }
                   steps++;
               }
               break;
           default:
               break;
           }
            if(steps>100000){
               end = true;
               System.out.println("The Robot is Stucked! try different Bord.");
           }
       }
       return currentBoard;
   }

   private static int turnLeft(int dir) {
       dir++;
       if(dir==5){
           dir = 1;
       }
       return dir;
   }

   private static int turnRight(int dir) {
       dir--;
       if(dir==0){
           dir = 4;
       }
       return dir;
   }

   public static int[] getRandomCoordinate(int maxY, int maxX) {
        int[] coor = new int[2];
        int y = r.nextInt(maxY);
        int x = r.nextInt(maxX);
        coor[0] = y;
        coor[1] = x;
        return coor;
    }
    public static char[][] createBoard(int row, int col) {
        if (row < 5 || col < 5) {
            throw new IllegalArgumentException("Both x and y axes must be greater than or equal to 5.");
        }
        char[][] board = new char[row][col];
        for (int i = 0; i < col; i++) {
            board[0][i] = '#';
        }
        for (int i = 1; i < row - 1; i++) {
            board[i][0] = '#';
            for (int j = 1; j < col - 1; j++) {
                board[i][j] = ' ';
            }
            board[i][col - 1] = '#';
        }
        for (int i = 0; i < col; i++) {
            board[row - 1][i] = '#';
        }
        board[1][1] = '.';
        board[row - 2][col - 2] = 'x';
        return board;
    }
    private static char[][] createRandomObstacle(char[][] board, int num) {
        int space = 0;

        for (int i = 0; i < board.length; i++) {
            for (int j = 0; j < board[i].length; j++) {
                if (board[i][j] == ' ') {
                    space += 1;
                }
            }
        }
        if (num > space) {
            throw new IllegalArgumentException("Too many obstacles");
        }
        for (int i = 0; i < num; i++) {
            int[] randCoord = getRandomCoordinate(board.length, board[0].length);
            while (board[randCoord[0]][randCoord[1]] != ' ') {
                randCoord = getRandomCoordinate(board.length, board[0].length);
            }
            board[randCoord[0]][randCoord[1]] = '#';
        }
        return board;
    }

    private static void displayBoard(char[][] board){
        for (int i = 0; i < board.length; i++) {
            for (int j = 0; j < board[i].length; j++) {
               if (board[i][j] != ' ') {
                    System.out.print(board[i][j]);
                }
            }
            System.out.println("");
        }
    }
}