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Hi there,

Say I have a 2D array, of which we are using as a gameboard for instance.

For example, a 5x5 2D array of the type char, and initialized with dots and a 'S'.

Java
char[][] array = new char[5][5]


.....
.....
..S..
.....
.....

How can I find the indexes of the 2D array that are closest to the letter S (aka wrap around it), in terms of proximity on the board, and then turn this into a new array?

So in this example, the 8 dots that surround S can now be initialized into a new array.


What I have tried:

I have tried finding the Euclidean distance between a given point and the array elements that surround it, and then attaching the objects of that array to a length by means of a hashmap. Note that the above question is more for simplicity sakes, and my actual project works with custom-type 2D arrays, evident in the code below. Nevertheless, the concept is still applicable.


Java
public static void getIndexes(Grid_23722002 grid, Piece_23722002 piece){

        int row = piece.getRow();
        int col = piece.getCol();

        Piece_23722002[][] nhood = new Piece_23722002[8][8];
        Map<Piece_23722002, Integer> unsortedLengthMap = new LinkedHashMap<Piece_23722002, Integer>();

        for (int i =0; i < grid.getArrayForm().length; i++){

            for (int j =0; j < grid.getArrayForm()[i].length; j++){

                unsortedLengthMap.put(piece, grid.getArrayForm()[i][j].getLengthToPoint(grid, i, j, piece));

            }

        }

        Map<Piece_23722002, Integer> sortedLengthMap = new LinkedHashMap<Piece_23722002, Integer>();
        unsortedLengthMap.entrySet()
                .stream()
                .sorted(Map.Entry.comparingByValue())
                .forEachOrdered(x -> sortedLengthMap.put(x.getKey(), x.getValue()));


    }

    public int getLengthToPoint(Grid_23722002 grid, int i, int j, Piece_23722002 piece){

        int piecesRow = piece.getRow();
        int piecesCol = piece.getCol();

        int length = (int) Math.sqrt(Math.pow(grid.getArrayForm()[i][j].getRow() - piecesRow, 2) + Math.pow(grid.getArrayForm()[i][j].getCol() - piecesCol, 2));

        return length;

    }
Posted
Updated 14-Sep-20 3:53am

1 solution

If you have a "point" (x,y) in a 2D array, then there can be "up to" 8 points surrounding the first point (less if the first point is on an "edge" of the array).

You determine "neighbors" for x,y as follows:

n = x, y+1
s = x, y-1
e = x+1, y
w = x-1, y
ne = x+1, y+1
nw = x-1, y+1
etc.

If any calculated x or y is less than 0 or greater than an upper array bound, the calculated point is "off the board".

I use a "class" for the points in my game; and made the "neighbors" children of each point so I only do those particular calcs once.

(For "border points" I still do the calcs but use a "dummy" point to represent the point outside the array ... just makes things easier. So, if your requirement is 5x5, use 7x7 and reserve the outside points for "out of bounds")
   
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