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Hi guys, I am having a problem to implement an algorithm to create an 8 puzzle program that uses uninformed search to find the solution for the puzzle. So far I have only made little progress using DFS.
The problem that I am facing now with the above code is that whenever the program pops the stack it does not tally with the value that has been push earlier in the swap function method (Puzzle Class).

Any help will be appreciated. Thanks. :)


What I have tried:

public class Main {
    public Main() {
    }

    public static void main(String args[]) {
        int startState[][] = {{6,2,5}, {1,8,0}, {7,4,3}}, goalState[][] = {{7,6,5}, {8,0,4}, {1,2,3}};

        System.out.println("Solving puzzle using DFS...");
        DFS dfs = new DFS(startState, goalState);
        dfs.search();
    }
}
import java.util.Stack;
import java.util.ArrayList;

public class DFS {
    private int moveCounter = 0;
    private Stack<Node> fringe = new Stack<Node>();
    private Node startState, goalState, currentState = new Node();
    private ArrayList<Node> closed = new ArrayList<Node>();

    public DFS(int start[][], int goal[][]) {
        startState = new Node(start);
        goalState = new Node(goal);
        fringe.push(startState);
    }

    private void succesor(Node currentState) {
        Node newState = new Node();
        Puzzle p = new Puzzle();

        newState = p.moveUp(currentState);

        if (newState != null) {
            fringe.push(newState);
        }

        newState = p.moveRight(currentState);

        if (newState != null) {
            fringe.push(newState);
        }

        newState = p.moveDown(currentState);

        if (newState != null) {
            fringe.push(newState);
        }

        newState = p.moveLeft(currentState);

        if (newState != null) {
            fringe.push(newState);
        }
    }

    public void search() {
        boolean found = false, exist = false, checkElement = true;
        Node tmpNode = new Node();

        currentState = fringe.pop();
        closed.add(currentState);
        succesor(currentState);

        for (int x = 1; x < 2 ; x++) {
            while (!found) {
                try {
                    currentState = fringe.pop();

                    for (int i = 0; i < closed.size(); i++) {
                        tmpNode = closed.get(i);

                        if (currentState.toString().equals(tmpNode.toString())) {
                            exist = true;
                            break;
                        }                        
                    }

                    if (!exist) {
                        moveCounter++;

                        if (currentState.getX(x) == goalState.getX(x) && currentState.getY(x) == goalState.getY(x)) {
                            found = true;
                            break;
                        }
                        else {
                            closed.add(currentState);
                            succesor(currentState);
                        }
                    }
                }
                catch (Exception e) {
                    System.out.println("No solutions found!");
                    break;
                }
            }
        }

        System.out.println("Number of step(s): " + moveCounter);
    }
}
public class Node {
    int state[][] = new int[3][3];
    
    public Node() {
    }
    
    public Node(int state[][]) {
        this.state = state;
    }
    
    public int getNum(int posX, int posY) {
        return state[posX][posY];
    }
    
    public void setNum(int num, int x, int y) {
        state[x][y] = num;
    }
    
    public int getX(int num) {
        int positionX = 0;

        for (int x = 0; x < 3; x++) {
            for (int y = 0; y < 3; y++) {
                if (state[x][y] == num) {
                    positionX = x;
                    break;
                }
            }
        }

        return positionX;
    }
    
    public int getY(int num) {
        int positionY = 0;

        for (int x = 0; x < 3; x++) {
            for (int y = 0; y < 3; y++) {
                if (state[x][y] == num) {
                    positionY = y;
                    break;
                }
            }
        }

        return positionY;
    }
    
    public void getCoordinate(int coordinate[], int num) {
        for (int x = 0; x < 3; x++) {
            for (int y = 0; y < 3; y++) {
                if (state[x][y] == num) {
                    coordinate[0] = x;
                    coordinate[1] = y;
                    break;
                }
            }
        }
    }
    
    public void getState(int state[][]) {
        state = this.state;
    }
    
    public String toString() {
        String output = "";

        for (int x = 0; x < 3; x++) {
            for (int y = 0; y < 3; y++) {
                output += state[x][y];
            }
            output += "\n";
        }

        return output;
    }
}
public class Puzzle {    
    public Puzzle() {
    }
    
    private void swap(Node newState, int newPosition[]) {
        int emptyTile[] = new int[2], tmpNum;                

        newState.getCoordinate(emptyTile, 0);
        tmpNum = newState.getNum(newPosition[0], newPosition[1]);
        
        newState.setNum(0, newPosition[0], newPosition[1]);
        newState.setNum(tmpNum, emptyTile[0], emptyTile[1]);
    }
        
    public Node moveUp(Node currentState) {
        Node newState = new Node();
        newState = null;
        int newPosition[] = new int[2];

        if (currentState.getX(0) - 1 >= 0) {
            newState = currentState;
            newPosition[0] = newState.getX(0) - 1;
            newPosition[1] = newState.getY(0);

            swap(newState, newPosition);
        }

        return newState;
    }        
        
    public Node moveRight(Node currentState) {
        Node newState = new Node();
        newState = null;
        int newPosition[] = new int[2];

        if (currentState.getY(0) + 1 <= 2) {
            newState = currentState;
            newPosition[0] = newState.getX(0);
            newPosition[1] = newState.getY(0) + 1;

            swap(newState, newPosition);
        }

        return newState;
    }        
        
    public Node moveDown(Node currentState) {
        Node newState = new Node();
        newState = null;
        int newPosition[] = new int[2];

        if (currentState.getX(0) + 1 <= 2) {
            newState = currentState;
            newPosition[0] = newState.getX(0) + 1;
            newPosition[1] = newState.getY(0);

            swap(newState, newPosition);
        }

        return newState;
    }        
        
    public Node moveLeft(Node currentState) {
        Node newState = new Node();
        newState = null;
        int newPosition[] = new int[2];

        if (currentState.getY(0) - 1 >= 0) {
            newState = currentState;
            newPosition[0] = newState.getX(0);
            newPosition[1] = newState.getY(0) - 1;

            swap(newState, newPosition);
        }

        return newState;
    }        
}
Posted
Updated 19-Mar-20 22:04pm

When you posted this question yesterday: Solve 8-puzzle in java[^] I told you to use the debugger:
Quote:
Compiling does not mean your code is right! :laugh:
Think of the development process as writing an email: compiling successfully means that you wrote the email in the right language - English, rather than German for example - not that the email contained the message you wanted to send.

So now you enter the second stage of development (in reality it's the fourth or fifth, but you'll come to the earlier stages later): Testing and Debugging.

Start by looking at what it does do, and how that differs from what you wanted. This is important, because it give you information as to why it's doing it. For example, if a program is intended to let the user enter a number and it doubles it and prints the answer, then if the input / output was like this:
Input   Expected output    Actual output
  1            2                 1
  2            4                 4
  3            6                 9
  4            8                16
Then it's fairly obvious that the problem is with the bit which doubles it - it's not adding itself to itself, or multiplying it by 2, it's multiplying it by itself and returning the square of the input.
So with that, you can look at the code and it's obvious that it's somewhere here:
C#
int Double(int value)
   {
   return value * value;
   }

Once you have an idea what might be going wrong, start using the debugger to find out why. Put a breakpoint on the first line of the method, and run your app. When it reaches the breakpoint, the debugger will stop, and hand control over to you. You can now run your code line-by-line (called "single stepping") and look at (or even change) variable contents as necessary (heck, you can even change the code and try again if you need to).
Think about what each line in the code should do before you execute it, and compare that to what it actually did when you use the "Step over" button to execute each line in turn. Did it do what you expect? If so, move on to the next line.
If not, why not? How does it differ?
Hopefully, that should help you locate which part of that code has a problem, and what the problem is.
This is a skill, and it's one which is well worth developing as it helps you in the real world as well as in development. And like all skills, it only improves by use!

That advice hasn't changed: this is part of your task - design code to meet the specification (your homework question provides that), implement, test, debug, revise, repeat until working.
And if you don't learn to debug your code with simple tasks like this, then you are going to be completely lost when you get to a larger code base: 100,000 lines for example.

So dig out the debugger, and start following your code through to find out exactly what it is doing!
 
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Quote:
The problem that I am facing now with the above code is that whenever the program pops the stack it does not tally with the value that has been push earlier in the swap function method (Puzzle Class).

Your code do not behave the way you expect, or you don't understand why !

There is an almost universal solution: Run your code on debugger step by step, inspect variables.
The debugger is here to show you what your code is doing and your task is to compare with what it should do.
There is no magic in the debugger, it don't know what your code is supposed to do, it don't find bugs, it just help you to by showing you what is going on. When the code don't do what is expected, you are close to a bug.
To see what your code is doing: Just set a breakpoint and see your code performing, the debugger allow you to execute lines 1 by 1 and to inspect variables as it execute.

Debugger - Wikipedia, the free encyclopedia[^]

Mastering Debugging in Visual Studio 2010 - A Beginner's Guide[^]
Basic Debugging with Visual Studio 2010 - YouTube[^]

http://docs.oracle.com/javase/7/docs/technotes/tools/windows/jdb.html[^]
https://www.jetbrains.com/idea/help/debugging-your-first-java-application.html[^]

The debugger is here to only show you what your code is doing and your task is to compare with what it should do.
 
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