Advent of Code 2023 - Day 3

day3.php

<?php

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

$input = "467..114..
...*......
..35..633.
......#...
617*......
.....+.58.
..592.....
......755.
...$.*....
.664.598..";

final readonly class PartNumber
{
    public function __construct(
        public int $value,
        public int $xStart,
        public int $xEnd,
        public int $y,
    ) {
    }

    public function isNextTo(Collection $symbols): bool
    {
        return $symbols
            ->filter(function (Symbol $symbol): bool {
                return $symbol->x >= $this->xStart - 1
                    && $symbol->x <= $this->xEnd + 1
                    && $symbol->y >= $this->y - 1
                    && $symbol->y <= $this->y + 1;
            })
            ->isNotEmpty();
    }
}

final readonly class Symbol
{
    public function __construct(
        public string $value,
        public int $x,
        public int $y,
    ) {
    }

    public function adjacentPartNumbers(Collection $partNumbers): Collection
    {
        return $partNumbers
            ->filter(function (PartNumber $partNumber): bool {
                $xRange = range($this->x - 1, $this->x + 1);
                $yRange = range($this->y - 1, $this->y + 1);

                return in_array($partNumber->y, $yRange)
                    && ! empty(array_intersect($xRange, range($partNumber->xStart, $partNumber->xEnd)));
            })
            ->values();
    }
}

$lines = Str::of($input)->explode("\n");

$symbols = $lines
    ->map(function (string $line, int $y): array {
        preg_match_all('/(?!\d+)(?!\.)./', $line, $symbols, PREG_OFFSET_CAPTURE);

        return Arr::map($symbols[0], static fn ($symbol) => new Symbol(
            value: $symbol[0],
            x: intval($symbol[1]),
            y: $y,
        ));
    })
    ->filter()
    ->flatten(1);

$gears = $symbols->filter(static fn (Symbol $symbol): bool => $symbol->value === '*');

$partNumbers = $lines
    ->map(function (string $line, int $y): array {
        preg_match_all('/\d+/', $line, $numbers, PREG_OFFSET_CAPTURE);

        return Arr::map($numbers[0], static fn ($number) => new PartNumber(
            value: intval($number[0]),
            xStart: $number[1],
            xEnd: $number[1] + (strlen($number[0]) - 1),
            y: $y,
        ));
    })
    ->filter()
    ->flatten(1);

$part1 = $partNumbers
    ->filter(static fn (PartNumber $partNumber): bool => $partNumber->isNextTo($symbols))
    ->map(static fn (PartNumber $partNumber): int => $partNumber->value)
    ->sum();

$part2 = $gears
    ->map(static fn (Symbol $gear): Collection => $gear->adjacentPartNumbers($partNumbers))
    ->filter(static fn (Collection $partNumbers): bool => $partNumbers->count() === 2)
    ->map(static fn (Collection $partNumbers): int => $partNumbers->first()->value * $partNumbers->last()->value)
    ->sum();

$day3 = [$part1, $part2];