Slider Puzzle in javaFX - Swapping a button if it borders on the blank button - javafx

Question

I am coding a slider puzzle, using a 2-D array of buttons where 1 button is blank at all times, and the remaining buttons can only move if they are next to the blank button. Would anyone be able to offer a way to check the surrounding buttons and determine if it borders on the blank one? (keeping in mind boundaries)

Answer 1

Create fields blankX and blankY that contain the current position of the blank.
For each button save the current position in the properties. This allows you to retrieve the coordinates of the button, check, if they are adjacent to the blank and swap the positions, if that's the case.
Example:
private int blankX = 0;
private int blankY = 0;
private static final int SIZE = 50;
private static final String X_KEY = "TileLocationX";
private static final String Y_KEY = "TileLocationY";
private void move(Node n, int x, int y) {
// adjust position
n.setLayoutX(blankX * SIZE);
n.setLayoutY(blankY * SIZE);
// save coordinates to property
n.getProperties().put(X_KEY, blankX);
n.getProperties().put(Y_KEY, blankY);
// save node pos as blank pos
blankX = x;
blankY = y;
}
#Override
public void start(Stage primaryStage) {
Pane pane = new Pane();
EventHandler<ActionEvent> handler = evt -> {
Node n = (Node) evt.getSource();
int x = (Integer) n.getProperties().get(X_KEY);
int y = (Integer) n.getProperties().get(Y_KEY);
if (Math.abs(x - blankX) + Math.abs(y - blankY) == 1) {
// move button, if it's adjacent to the blank
move(n, x, y);
}
};
int count = 1;
// create grid
for (int i = 0; i < 5; i++) {
for (int j = 0; j < 5; j++) {
if (i != blankX || j != blankY) {
Button button = new Button(Integer.toString(count++));
button.setPrefSize(SIZE, SIZE);
button.setLayoutX(SIZE * i);
button.setLayoutY(SIZE * j);
button.getProperties().put(X_KEY, i);
button.getProperties().put(Y_KEY, j);
button.setOnAction(handler);
pane.getChildren().add(button);
}
}
}
Scene scene = new Scene(pane);
primaryStage.setScene(scene);
primaryStage.show();
}

Answer 2

2D arrays make it easy. Check for null above, below, right, and left, making sure that you aren't going out of bounds (aka checking boxes off the actual game grid).
I'm not sure if JavaFX is different from Java, so I can only give pseudo code:
//initialize int[5][5] (position) with tile classes (Tile), setting one to null
//checking tile at position[a][b]
//check position[a-1][b], [a+1][b], [a][b-1], [a][b+1] for null...
//...also making sure the value is between 0 and 5
//if any of those is true, square is moveable!
There might be an even more efficient way to do this, however. If you add another variable (boolean isMoveable) to each tile, then you can start each turn by finding the empty square and simply checking off every tile it borders as moveable. This would even allow you to highlight them somehow at the beginning of the turn, so the player knows what he can move.
And if you don't want to search through the entire board for the empty square, you can simply do it once at the beginning and save it's position to an array. Next turn, look to each square bordering that position to find the empty one.

Answer 3

If you have a 2D array, then you have the x and y location of each button. Keep the location of the blank button in variables, say blankX and blankY.
Then the condition for a button to be adjacent to the blank button is
Either x==blankX and y and blankY differ by 1, or
y==blankY and x and blankX differ by 1
So if you do
int deltaX = Math.abs(x - blankX) ;
int deltaY = Math.abs(y - blankY) ;
the condition is
deltaX==0 && deltaY==1, or
deltaX==1 && deltaY==0
but since deltaX >= 0 and deltaY >= 0, this is just equivalent to
deltaX + deltaY == 1
If you make blankX and blankY JavaFX properties:
private final IntegerProperty blankX = new SimpleIntegerProperty();
private final IntegerProperty blankY = new SimpleIntegerProperty();
then you can easily disable the button when it's not adjacent to the blank buttons:
// creates a button with coordinates x,y and initializes it
private Button createButton(int x, int y) {
Button button = new Button(Integer.toString(x + y * numColumns + 1));
// disable if not adjacent to blank button:
button.disableProperty().bind(Bindings.createBooleanBinding(
() -> Math.abs(x - blankX.get()) + Math.abs(y - blankY.get()) != 1,
blankX, blankY));
// when pressed, swap with blank button and update blankX, blankY:
button.setOnAction(e -> {
buttonArray[blankX.get()][blankY.get()].setText(button.getText());
button.setText("");
blankX.set(x);
blankY.set(y);
});
return button ;
}