Advent of code 2021/10

Ajax Direct

// Remove all matching pairs
$lines = $input->lines->map(function ($line) {
    $pairs = ["[]", "()", "{}", "<>"];
    for ($i = 0; $i < $line->length() / 2 + 2; $i++) {
        $line = $line->replace($pairs, "");
    }
    return $line;
});

// ==================================================
// > PART 1
// ==================================================
$invalid = $lines->map(fn ($line) => [
    ")" => 3,
    "]" => 57,
    "}" => 1197,
    ">" => 25137,
][$line->match("/[\)\]\}\>]/")[0] ?? null] ?? 0);

$solution_1 = $invalid->sum();

// ==================================================
// > PART 2
// ==================================================
$incomplete = $lines->removeKeys($invalid->filter()->keys());

$scores = $incomplete->map(fn ($open) =>
    $open->chars()->reverse()->reduce(fn ($score, $open) =>
        ($score * 5) + [
            "(" => 1,
            "[" => 2,
            "{" => 3,
            "<" => 4,
        ][$open]
    , 0)
);

$solution_2 = $scores->sort()->values()[floor($scores->count() / 2)];