Advent of Code 2023 - Day 11

day11.php

<?php

declare(strict_types=1);

use Illuminate\Support\Arr;
use Illuminate\Support\Collection;
use Illuminate\Support\Str;

$input = "...#......
.......#..
#.........
..........
......#...
.#........
.........#
..........
.......#..
#...#.....";

final readonly class Galaxies
{
    public function __construct(
        public int $x,
        public int $y,
    ) {
    }

    public function distance(Galaxies $other, Collection $emptyColumns, Collection $emptyRows, int $multiplier): int
    {
        $emptyColumnCount = $emptyColumns
            ->filter(fn (int $row): bool => $row > min($this->x, $other->x) && $row < max($this->x, $other->x))
            ->count();

        $emptyRowCount = $emptyRows
            ->filter(fn (int $row): bool => $row > min($this->y, $other->y) && $row < max($this->y, $other->y))
            ->count();

        return abs($this->x - $other->x) + ($emptyColumnCount * $multiplier - $emptyColumnCount)
            + abs($this->y - $other->y) + ($emptyRowCount * $multiplier - $emptyRowCount);
    }
}

$rows = Str::of($input)->explode(PHP_EOL);

$galaxies = $rows
    ->map(static function (string $line, int $y): array {
        preg_match_all('/#/', $line, $matches, PREG_OFFSET_CAPTURE);

        return Arr::map($matches[0], static fn (array $galaxies) => new Galaxies($galaxies[1], $y));
    })
    ->flatten(1)
    ->sortBy(['y', 'x'])
    ->values();

$emptyColumns = Collection::range(0, strlen($rows->first()) - 1)
    ->diff(
        $galaxies
        ->map(static fn (Galaxies $galaxies): int => $galaxies->x)
        ->unique()
        ->sort()
        ->values(),
    )
    ->values();

$emptyRows = Collection::range(0, $rows->count() - 1)
    ->diff(
        $galaxies
        ->map(static fn (Galaxies $galaxies): int => $galaxies->y)
        ->unique()
        ->sort()
        ->values(),
    )
    ->values();

$combos = $galaxies->reduce(
    static function (Collection $combos, Galaxies $left, int $index) use ($galaxies) {
        $galaxies
            ->skip($index + 1)
            ->each(static fn (Galaxies $right) => $combos->add([$left, $right]));

        return $combos;
    },
    new Collection(),
);

$part1 = $combos
    ->reduce(static function (int $sum, array $combo) use ($emptyColumns, $emptyRows): int {
        [$left, $right] = $combo;

        return $sum + $left->distance($right, $emptyColumns, $emptyRows, 2);
    }, 0);


$part2 = $combos
    ->reduce(static function (int $sum, array $combo) use ($emptyColumns, $emptyRows): int {
        [$left, $right] = $combo;

        return $sum + $left->distance($right, $emptyColumns, $emptyRows, 1000000);
    }, 0);

$result = [$part1, $part2];