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Thread: BackTracking in a maze

  1. #1
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    Default BackTracking in a maze

    Hello every body

    I'm creating a program that generates a random maze depending on the starting point you enter and then solves it. My problem is that even thought there is a solution to the maze, it returns that there is no solution to the maze.

    I know that I have to do backtracking in the getMove() method but I don't know how to do it

    this is my code

        import java.io.*;
        import java.util.*;
        import java.util.ArrayList;
     
        public class lab29a
        {
    	    public static void main(String args[]) throws IOException
    	    {
    		    System.out.println("\nLab 29a \n");
    		    BufferedReader input = new BufferedReader(new InputStreamReader(System.in));
    		    System.out.print("Enter random starting seed  ===>>  ");
    		    int seed = Integer.parseInt(input.readLine());
     
    		    Maze maze = new Maze(seed);
    		    maze.displayMaze();
    		    maze.solveMaze();
    		    maze.displayMaze();
    		    maze.mazeSolution();
    	    }
        }
     
        class Coord  	// Coord is a class that stores a single maze location.
        {
    	    private int rPos;
    	    private int cPos;
    	    public Coord (int r, int c) 	{ rPos = r; cPos = c; }
    	    public boolean isFree() 		{ return (rPos == 0 && cPos == 0);}               
    	    public void setPos(int r, int c) 	{ rPos+= r; cPos+= c; }
            public int getrPos() 	        { return  rPos;   }
            public int getcPos() 	        { return  cPos;   }
        }
     
        class Maze
        {
    	    private char mat[][];			// 2d character array that stores the maze display
    	    private Coord currentMove;		// object that stores current maze position
    	    private MyStack visitStack;		// stack that stores location that have been visited
     
    	    // constructor which generates the random maze, random starting location
    	    // and initializes Maze class values.  If the random value equals 0 the maze
    	    // store an 'X' otherwise it store an 'O' in the maze.
    	    public Maze(int seed)
    	    {
    		    Random random = new Random(seed);
    		    int startRow, startCol;
    		    mat = new char[12][12];
    		    for (int r = 0; r < 12; r++)
    			    for (int c = 0; c < 12; c++)
    			    {
    				    if (r == 0 || c == 0 || r == 11 || c == 11)
    					    mat[r][c] = 'X';
    				    else
    				    {
    					    int rndInt = random.nextInt(2);
    					    if (rndInt == 0)
    						    mat[r][c] = 'X';
    					    else
    						    mat[r][c] = 'O';
    				    }
    			    }
    		    mat[0][0] = 'O';
    		    startRow = random.nextInt(12);
    		    startCol = 11;
    		    mat[startRow][startCol] = '.';
    		    visitStack = new  MyStack();
    		    currentMove = new Coord(startRow,startCol);
    		    visitStack.push(currentMove);
    	    }
     
    	    // displays the current maze configuration
    	    void displayMaze() throws IOException
    	    {
    		    System.out.println("\nRANDOM MAZE DISPLAY\n");
    		    for (int r = 0; r < 12; r++)
    		    {
    			    for (int c = 0; c < 12; c++)
    				    System.out.print(mat[r][c] + "  ");
    			    System.out.println();
    		    }
    		    System.out.println();
    		    pause();
    	    }
     
    	    // This method solves the maze with private helper method <getMove>.
    	    // A loop is needed to repeat getting new moves until either a maze solution
    	    // is found or it is determined that there is no way out off the maze.
    	    public void solveMaze() throws IOException
    	    {
    		    System.out.println("\n>>>>>   WORKING  ....  SOLVING MAZE   <<<<<\n");
     
    		    while(getMove())
    		    {
    				mat[currentMove.getrPos()][currentMove.getcPos()] = '.';
    		    }
    	    }
     
    	    // Short method to display the result of the maze solution
    	    public void mazeSolution()
    	    {
    		    if (currentMove.isFree())
    			    System.out.println("\nTHE MAZE HAS A SOLUTION.\n");
    		    else
    			    System.out.println("\nTHE MAZE HAS NO SOLUTION.\n");
    	    }
     
    	    // This method determines if a coordinate position is inbounds or not
    	    private boolean inBounds(int r, int c)
    	    {
    		    boolean inBound = false;
     
    		    if(r >= 0 && c >= 0)
    		    {
    			    if((r + 1 ) < mat.length && (c + 1) < mat[0].length)
    				    inBound = true;
    		    }
     
    		    return inBound;
    	    }
     
       	    // This method checks eight possible positions in a counter-clock wise manner
    	    // starting with the (-1,0) position.  If a position is found the method returns
    	    // true and the currentMove coordinates are altered to the new position
    	    private boolean getMove() throws IOException
    	    {
    		    boolean canmove = false;
    		    int tempRow = currentMove.getrPos();
    		    int tempCol = currentMove.getcPos();
     
    		    if(inBounds((currentMove.getrPos() - 1), (currentMove.getcPos() + 0)) == true)
    		    {
    			    if(mat[currentMove.getrPos() - 1][currentMove.getcPos() + 0] == 'O')
    			    {
    				    canmove = true;
     
    				    tempRow = currentMove.getrPos() - 1;
    				    tempCol = currentMove.getcPos() + 0;
    			    }
    		    }
     
    		    if(inBounds((currentMove.getrPos() -1), (currentMove.getcPos() +1)) == true)
    		    {
    			    if(mat[currentMove.getrPos() - 1][currentMove.getcPos() + 1] == 'O')
    			    {
    				    canmove = true;
     
    				    tempRow = currentMove.getrPos() - 1;
    				    tempCol = currentMove.getcPos() + 1;
    			    }
    		    }
     
    		    if(inBounds((currentMove.getrPos() + 0), (currentMove.getcPos() + 1)) == true)    
    		    {
    			    if(mat[currentMove.getrPos() + 0][currentMove.getcPos() + 1] == 'O')
    			    {
    				    canmove = true;
     
    				    tempRow = currentMove.getrPos() + 0;
    				    tempCol = currentMove.getcPos() + 1;
    			    }
    		    }
     
    		    if(inBounds((currentMove.getrPos() + 1), (currentMove.getcPos() + 1)) == true)
    		    {
    			    if(mat[currentMove.getrPos() + 1][currentMove.getcPos() + 1] == 'O')
    			    {    
    				    canmove = true;
     
    				    tempRow = currentMove.getrPos() + 1;
    				    tempCol = currentMove.getcPos() + 1;
    			    }
    		    }
     
    		    if(inBounds((currentMove.getrPos() + 1), (currentMove.getcPos() + 0)) == true)
    		    {
    			    if(mat[currentMove.getrPos() + 1][currentMove.getcPos() + 0] == 'O')
    			    {
    				    canmove = true;
     
    				    tempRow = currentMove.getrPos() + 1;
    				    tempCol = currentMove.getcPos() + 0;
    			    }
    		    }
     
    		    if(inBounds((currentMove.getrPos() + 1), (currentMove.getcPos() - 1)) == true)
    		    {
    			    if(mat[currentMove.getrPos() + 1][currentMove.getcPos() - 1] == 'O')
    			    {
    				    canmove = true;
     
    				    tempRow = currentMove.getrPos() + 1;
    				    tempCol = currentMove.getcPos() - 1;
    			    }
    		    }
     
    		    if(inBounds((currentMove.getrPos() + 0), (currentMove.getcPos() - 1)) == true)
    		    {
    			    if(mat[currentMove.getrPos() + 0][currentMove.getcPos() - 1] == 'O')
    			    {
    				    canmove = true;
     
    				    tempRow = currentMove.getrPos() + 0;
    				    tempCol = currentMove.getcPos() - 1;
    			    }
    		    }
     
    		    if(inBounds((currentMove.getrPos() - 1), (currentMove.getcPos() - 1)) == true)
    		    {
    			    if(mat[currentMove.getrPos() - 1][currentMove.getcPos() - 1] == 'O')
    			    {
    				    canmove = true;
     
    				    tempRow = currentMove.getrPos() - 1;
    				    tempCol = currentMove.getcPos() - 1;
    			    }
    		    }
     
    		    currentMove = new Coord(tempRow, tempCol);
     
    		    return canmove;
    	    }
     
    	    private void pause() throws IOException
    	    {
    		    BufferedReader input = new BufferedReader(new InputStreamReader(System.in));
    		    String dummy;
    		    System.out.print("\nPress <Enter> to continue  ===>>  ");
    		    dummy = input.readLine();
    	    }
        }
     
     
     
        class MyStack<E>
        {
    	    private ArrayList<E> data;	// stores stack data
    	    private int top;				// keeps index of the stack top
     
    	    public MyStack()
    	    // Initializes an empty array object with references of private variable data objects.
    	    {
    		    data = new ArrayList<E>();
    		    top = -1;
    	    }
     
    	    public boolean isEmpty()
    	    // Returns true if data is empty, false otherwise
    	    {
    		    return top == -1;
    	    }
     
    	    public void push (E x)
    	    // Adds variable x to the top of the stack
    	    {
    		    data.add(x);
    		    top++;
    	    }
     
    	    public E pop()
    	    // Returns and removes the top element from the stack
    	    {
    		    int temp = top;
    		    top--;
    		    return data.remove(temp);
    	    }
     
    	    public E peek()
    	    // Returns the top element from the stack without removal
    	    {
    		    return data.get(top);
    	    }
     
        }


    this is my output

    X - SOLID WALL (no passage allowed)

    O - PATH (passage allowed)

    . - TRAVELED (path traveled to find the exit)

        Enter random starting seed  ===>>  25
     
        RANDOM MAZE DISPLAY
     
        O  X  X  X  X  X  X  X  X  X  X  X
        X  O  O  X  O  O  X  X  X  X  X  X
        X  O  O  X  O  X  O  X  O  O  O  X
        X  X  X  O  O  X  X  O  O  O  X  X
        X  X  X  X  O  O  O  O  O  X  O  X
        X  X  X  X  O  O  O  X  X  X  X  X
        X  O  X  O  X  X  O  X  O  X  O  X
        X  X  X  X  X  O  O  X  X  X  O  X
        X  X  X  O  O  X  X  O  O  X  O  X
        X  O  X  X  O  O  O  X  O  O  O  X
        X  X  X  X  X  O  O  X  O  X  O  .
        X  X  X  X  X  X  X  X  X  X  X  X
     
     
        Press <Enter> to continue  ===>>
     
        >>>>>   WORKING  ....  SOLVING MAZE   <<<<<
     
     
        RANDOM MAZE DISPLAY
     
        O  X  X  X  X  X  X  X  X  X  X  X
        X  O  O  X  O  O  X  X  X  X  X  X
        X  O  O  X  O  X  O  X  O  O  O  X
        X  X  X  O  O  X  X  O  O  O  X  X
        X  X  X  X  O  O  O  O  O  X  O  X
        X  X  X  X  O  O  O  X  X  X  X  X
        X  O  X  O  X  X  O  X  O  X  O  X
        X  X  X  X  X  .  .  X  X  X  O  X
        X  X  X  .  .  X  X  .  .  X  O  X
        X  O  X  X  .  .  .  X  O  .  .  X
        X  X  X  X  X  .  .  X  O  X  O  .
        X  X  X  X  X  X  X  X  X  X  X  X
     
     
        Press <Enter> to continue  ===>>
     
        THE MAZE HAS NO SOLUTION.
     
        Press any key to continue...



    this is what should the output be
        Enter random starting seed ===>> 25
     
        RANDOM MAZE DISPLAY
     
        O X X X X X X X X X X X
        X O O X O O X X X X X X
        X O O X O X O X O O O X
        X X X O O X X O O O X X
        X X X X O O O O O X O X
        X X X X O O O X X X X X
        X O X O X X O X O X O X
        X X X X X O O X X X O X
        X X X O O X X O O X O X
        X O X X O O O X O O O X
        X X X X X O O X O X O .
        X X X X X X X X X X X X
     
        Press <Enter> to continue ===>>
     
        >>>>> WORKING .... SOLVING MAZE <<<<<
     
        RANDOM MAZE DISPLAY
     
        . X X X X X X X X X X X
        X . . X . . X X X X X X
        X . . X . X . X . . . X
        X X X . . X X . . . X X
        X X X X . . . . . X . X
        X X X X . . . X X X X X
        X O X O X X . X O X . X
        X X X X X . O X X X . X
        X X X O . X X . . X . X
        X O X X . . . X . . . X
        X X X X X . . X . X . .
        X X X X X X X X X X X X
     
        Press <Enter> to continue ===>>
     
        THE MAZE HAS A SOLUTION.



    please help me for I need to know how to fix the program very quickly

    I would appreciate any answer or comment

    thank you in advance


  2. #2
    Super Moderator Norm's Avatar
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    Default Re: BackTracking in a maze

    One way I can think of is to use a recursive nextMove search method that tries all possible next squares from the current one. Any path that dead ends, stops running.
    Another would be to use a stack to keep track of the last position to allow you to back up if the current path was blocked.

    Is this a continuation of problem with a maze program

    I see that you didn't follow any of my suggestions from that post to make your code easier to debug.
    Last edited by Norm; January 26th, 2012 at 06:25 AM.

  3. #3
    Super Moderator Norm's Avatar
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    Default Re: BackTracking in a maze

    Cross posted at BackTracking in a maze - Java | DaniWeb

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