java - Find elements surrounding an element in an array

Question

I have a multidimensional array, I want to get the elements surrounding a particular element in that array.

For example if I have the following:

[[1,2,3,4,5,6]
 [8,9,7,5,2,6]
 [1,6,8,7,5,8]
 [2,7,9,5,4,3]
 [9,6,7,5,2,1]
 [4,7,5,2,1,3]]

How do I find all the 8 elements around any of the above elements? And how do I take care of elements at the edges?

One way I figured out is, to write a 9 line code for this , which is obvious, but is there a better solution?

Answer 1

You can use 'direction array' in form

[[-1,-1], [-1,0],[1,0]..and so on]

And method which takes point coordinate and iterates through direction array -> add direction numbers to coordinates, check indexes are not out of bounds and collect results. Something like this:

private static int[][] directions = new int[][]{{-1,-1}, {-1,0}, {-1,1},  {0,1}, {1,1},  {1,0},  {1,-1},  {0, -1}};

static List<Integer> getSurroundings(int[][] matrix, int x, int y){
    List<Integer> res = new ArrayList<Integer>();
    for (int[] direction : directions) {
        int cx = x + direction[0];
        int cy = y + direction[1];
        if(cy >=0 && cy < matrix.length)
            if(cx >= 0 && cx < matrix[cy].length)
                res.add(matrix[cy][cx]);
    }
    return res;
}