Advent of code 2023/16

Ajax Direct

function solve($start, $grid) {
    $queue = [$start];
    while ($queue) {
        [$x, $y, $dir] = array_shift($queue);
        if (isset($seen["$x;$y;$dir"])) continue;
        $seen["$x;$y;$dir"] = true;
        $enerygized["$x;$y"] = true;

        $dirs = match ($grid[$y][$x]) {
            "-" => match($dir) {"v", "^" => ["<", ">"], default => [$dir]},
            "|" => match($dir) {">", "<" => ["^", "v"], default => [$dir]},
            "/" => [[">" => "^", "<" => "v", "^" => ">", "v" => "<"][$dir]],
            "\\" => [[">" => "v", "<" => "^", "^" => "<", "v" => ">"][$dir]],
            default => [$dir]
        };

        foreach ($dirs as $dir) {
            [$nx, $ny] = match ($dir) {
                ">" => [$x + 1, $y],
                "<" => [$x - 1, $y],
                "^" => [$x, $y - 1],
                default => [$x, $y + 1],
            };
            if (!isset($grid[$ny][$nx])) continue;
            $queue[] = [$nx, $ny, $dir];
        }
    }
    return count($enerygized);
}

// ==================================================
// > PART 1
// ==================================================
$grid = array_map("str_split", explode("\n", $input));
$solution_1 = solve([0, 0, ">"], $grid);

// ==================================================
// > PART 2
// ==================================================
foreach (range(0, count($grid) - 1) as $y) {
    $s[] = solve([0, $y, ">"], $grid);
    $s[] = solve([count($grid) - 1, $y, "<"], $grid);
}
foreach (range(0, count($grid[0]) - 1) as $x) {
    $s[] = solve([$x, 0, "v"], $grid);
    $s[] = solve([$x, count($grid[0]) - 1, "^"], $grid);
}
$solution_2 = max($s);