Day5.php

<?php

declare(strict_types=1);

namespace App\Days;

use App\Contracts\Day;
use Illuminate\Support\Collection;
use RuntimeException;

class Day5 extends Day
{
    public const EXAMPLE1 = <<<eof
            [D]    
        [N] [C]    
        [Z] [M] [P]
         1   2   3 
        
        move 1 from 2 to 1
        move 3 from 1 to 3
        move 2 from 2 to 1
        move 1 from 1 to 2
        eof;

    /**
     * After the rearrangement procedure completes, what crate ends up on top of each stack?
     */
    public function solvePart1(mixed $input): int|string|null
    {
        $input = $this->parseInput($input);
        /** @var Collection $diagram */
        $diagram = $input->get('diagram');
        /** @var Collection $instructions */
        $instructions = $input->get('instructions');

        while ($instructions->isNotEmpty()) {
            $instruction = (string) $instructions->shift();
            preg_match("/move (\d+) from (\d+) to (\d+)/", $instruction, $matches);
            if (4 === count($matches)) {
                [, $amount, $from, $to] = $matches;
                $amount                 = (int) $amount;
                // move the crates one at a time
                while ($amount > 0) {
                    --$amount;

                    /** @var Collection $fromStack */
                    $fromStack = $diagram->get($from);
                    /** @var Collection $toStack */
                    $toStack = $diagram->get($to);

                    $crate = $fromStack->pop();
                    $toStack->push($crate);
                }
            }
        }

        return $diagram->map(fn ($stack) => $stack->pop())->implode('');
    }

    /**
     * After the rearrangement procedure completes, what crate ends up on top of each stack?
     */
    public function solvePart2(mixed $input): int|string|null
    {
        $input = $this->parseInput($input);
        /** @var Collection $diagram */
        $diagram = $input->get('diagram');
        /** @var Collection $instructions */
        $instructions = $input->get('instructions');

        while ($instructions->isNotEmpty()) {
            $instruction = (string) $instructions->shift();
            preg_match("/move (\d+) from (\d+) to (\d+)/", $instruction, $matches);
            if (4 === count($matches)) {
                [, $amount, $from, $to] = $matches;
                $amount                 = (int) $amount;

                /** @var Collection $fromStack */
                $fromStack = $diagram->get($from);
                /** @var Collection $toStack */
                $toStack = $diagram->get($to);

                // move the crates in bulk preserving the original order
                $fromStack->splice(-$amount)->each(fn ($item) => $toStack->push($item));
            }
        }

        return $diagram->map(fn ($stack) => $stack->pop())->implode('');
    }

    protected function parseInput(mixed $input): Collection
    {
        $input = is_array($input) ? $input : explode("\n", $input);

        return collect($input)
            ->chunkWhile(fn ($value) => '' !== $value)
            ->map(fn ($chunk) => $chunk->filter(fn ($value) => '' !== $value)->values())
            ->flatMap(fn ($chunk, $index) => 0 === $index
                ? ['diagram' => $this->setupDiagram($chunk)]
                : ['instructions' => collect($chunk)]);
    }

    protected function setupDiagram(Collection $rawDiagram): Collection
    {
        $stackLine = $rawDiagram->pop(); //  " 1   2   3 "
        // create an empty array keyed by the stack columns 1,2,3 etc
        $stackNumbers = preg_split("/\s+/", trim((string) $stackLine));
        if (false === $stackNumbers) {
            throw new RuntimeException('Failed to parse stack numbers');
        }
        /** @var array<string, array<int, string>> $stacks */
        $stacks = array_map(fn () => [], array_flip($stackNumbers));
        // loop over each remaining diagram line, adding the crates to the correct stack column
        $rawDiagram->each(function ($line) use (&$stacks): void {
            $crates = collect(mb_str_split($line, 4))
                ->map(fn ($char) => trim(str_replace(['[', ']'], '', $char)));
            foreach ($stacks as &$stack) {
                $crate = $crates->shift();
                if ('' !== $crate) {
                    $stack[] = $crate;
                }
            }
        });
        foreach ($stacks as &$stack) {
            $stack = collect(array_reverse($stack));
        }

        return collect($stacks);
    }
}