How to select adjacent tiles on a 5x5 board (6x6, doesn't matter)?

Question

PHP

I am doing a task, the task is to select all neighboring cells for a 5 by 5 board

First I just select all the neighbors

// Вертикальные соседи
        $nord = $blockIdFromClick - $n;
        $south = $blockIdFromClick + $n;

        // Горизонтальные
        $west = $blockIdFromClick - 1;
        $east = $blockIdFromClick + 1;

        // По диагонали (из правого верхнего угла)
        $nordEast = $blockIdFromClick - ($n-1);
        $southWest = $blockIdFromClick + ($n-1);

        // По диагонали (из левого верхнего угла)
        $nordWest = $blockIdFromClick - ($n+1);
        $southEast = $blockIdFromClick + ($n+1)

How to be with cages on the edges? Is there any algorithm?
And then it comes to mind only comparing the remainder of dividing the number by the bit depth of the grid (in this case 5) :)

Answer 1

Let's assume that the input is the coordinates of the central cell and the dimensions of the field, and the coordinates are counted from 0,0.
For the top and bottom lines, we check if it goes beyond the bounds. Inside the line, we check if there is a horizontal overflow.
Something like this:

/**
 * @param int $x center
 * @param int $y center
 * @param int $width
 * @param int $height
 */
function getNeighbours($x, $y, $width, $height) {
    $result = [];

    // 1st row
    if ($y > 0) {
        $rowY = $y - 1;
        $result[0] = $x > 0 ? [$x - 1, $rowY] : null;
        $result[1] = [$x, $rowY];
        $result[2] = $x < $width - 1 ? [$x + 1, $rowY] : null;
    } else {
        $result[0] = $result[1] = $result[2] = null;
    }

    // 2nd row
    $rowY = $y;
    $result[3] = $x > 0 ? [$x - 1, $rowY] : null;
    $result[4] = [$x, $rowY];
    $result[5] = $x < $width - 1 ? [$x + 1, $rowY] : null;

    // 3rd row
    if ($y < $height) {
        $rowY = $y + 1;
        $result[6] = $x > 0 ? [$x - 1, $rowY] : null;
        $result[7] = [$x, $rowY];
        $result[8] = $x < $width - 1 ? [$x + 1, $rowY] : null;
    } else {
        $result[6] = $result[7] = $result[8] = null;
    }

    return $result;
}

Example1

getNeighbours(5, 7, 10, 10);

Array
(
    [0] => Array
        (
            [0] => 4
            [1] => 6
        )

    [1] => Array
        (
            [0] => 5
            [1] => 6
        )

    [2] => Array
        (
            [0] => 6
            [1] => 6
        )

    [3] => Array
        (
            [0] => 4
            [1] => 7
        )

    [4] => Array
        (
            [0] => 5
            [1] => 7
        )

    [5] => Array
        (
            [0] => 6
            [1] => 7
        )

    [6] => Array
        (
            [0] => 4
            [1] => 8
        )

    [7] => Array
        (
            [0] => 5
            [1] => 8
        )

    [8] => Array
        (
            [0] => 6
            [1] => 8
        )

)

Example2

getNeighbours(5, 3, 5, 5);

Array
(
    [0] => Array
        (
            [0] => 4
            [1] => 2
        )

    [1] => Array
        (
            [0] => 5
            [1] => 2
        )

    [2] => 
    [3] => Array
        (
            [0] => 4
            [1] => 3
        )

    [4] => Array
        (
            [0] => 5
            [1] => 3
        )

    [5] => 
    [6] => Array
        (
            [0] => 4
            [1] => 4
        )

    [7] => Array
        (
            [0] => 5
            [1] => 4
        )

    [8] => 
)

Answer 2

Well, it comes to your mind. This is if the edges of the board are, as it were, glued together. If not, then just compare with the dimension of the board.