Advent of code 2018/11

Ajax Direct

$grid = [];

// Build the grid
for ($x = 1; $x <= 300; $x++) {
    for ($y = 1; $y <= 300; $y++) {
        $power = (($x + 10) * $y + $input->int) * ($x + 10);
        $power = (int) $power < 100 ? 0 : substr($power, -3, 1);
        $grid[$y][$x] = $power - 5;
    }
}

function find_best_square($grid, $size = 3) {
    $max_power = 0;
    $position  = null;

    for ($x = 1; $x <= 300 - $size + 1; $x++) {
        for ($y = 1; $y <= 300 - $size + 1; $y++) {
            $power = 0;
            for ($i = 0; $i < $size; $i++) {
                for ($j = 0; $j < $size; $j++) {
                    $power += $grid[$y + $i][$x + $j];
                }
            }
            if ($power > $max_power) {
                $max_power = $power;
                $position = "$x,$y";
            }
        }
    }

    return [$position, $max_power];
}

// ==================================================
// > PART 1
// ==================================================
$solution_1 = find_best_square($grid, 3)[0];

// ==================================================
// > PART 2
// ==================================================
$max_power = 0;
foreach (range(13, 17) as $size) { // Search in predefined range of sizes
    $found = find_best_square($grid, $size);
    if ($found[1] > $max_power) {
        $max_power = $found[1];
        $solution_2 = [$found[0] . ",$size", $max_power];
    }
}