Advent of Code - day 8

day8.php

<?php
declare(strict_types=1);

//$input = file('sample.txt', FILE_IGNORE_NEW_LINES);
//$input = file('sample-part2.txt', FILE_IGNORE_NEW_LINES);
$input = file('input.txt', FILE_IGNORE_NEW_LINES);

$instructions = $input[0];
printf('Instructions for %d lines: %s' . PHP_EOL, count($input) - 2, $instructions);
$nodes = parseNodes(array_slice($input, 2));

$startingNodes = findStartingNodes($nodes);
printf('Found %d nodes ending in "A"! (%s)' . PHP_EOL, count($startingNodes), implode(',', $startingNodes));
$stepsToZForNode = [];
foreach ($startingNodes as $startingNode) {
    $stepsToZForNode[] = findStepsToZForNode($startingNode, $nodes, $instructions);
}
printf('Found steps to Z for all nodes (%s), and the LCM is: %s' . PHP_EOL,
    implode(',', $startingNodes),
    getLcmForArray($stepsToZForNode)
);

function getLcmForArray(array $numbers): GMP
{
    if (count($numbers) === 2) {
        return gmp_lcm($numbers[0], $numbers[1]);
    }

    $num = array_shift($numbers);
    return gmp_lcm($num, getLcmForArray($numbers));
}

function findStepsToZForNode(string $startingNode, array $allNodes, string $instructions): int
{
    printf('Starting at node: %s' . PHP_EOL, $startingNode);
    $nextNode = $startingNode;
    $stepsDone = 0;
    for ($i = 0; true; $i++) {
        if ($i >= strlen($instructions)) {
            $i = 0;
        }
        $instruction = substr($instructions, $i, 1);
        $nextNode = $allNodes[$nextNode][$instruction];
        $stepsDone++;
        //printf('Next instruction is %s, pointing to node %s' . PHP_EOL, $instruction, $nextNode);

        if (substr($nextNode, -1, 1) === 'Z') {
            printf('Node %s points to node %s after %s steps' . PHP_EOL,
                $startingNode,
                $nextNode,
                $stepsDone
            );
            return $stepsDone;
        }
    }
}

function findStartingNodes(array $nodes): array
{
    $foundNodes = [];
    foreach ($nodes as $node => $nextNodes) {
        if (substr($node, -1, 1) === 'A') {
            $foundNodes[] = $node;
        }
    }

    return $foundNodes;
}

/*
 *  PART THE FIRST
 *
$currentStep = 0;
$currentNode = 'AAA';
$nextInstruction = getNextInstruction($instructions, $currentStep);
printf('Starting! First node: %s' . PHP_EOL, $currentNode);
while ($currentNode !== 'ZZZ') {
    $currentStep++;
    $nextNode = $nodes[$currentNode][$nextInstruction];
    printf('Choosing %s node: %s' . PHP_EOL, $nextInstruction, $nextNode);
    $nextInstruction = getNextInstruction($instructions, $currentStep);
    $currentNode = $nextNode;

    if ($currentStep > 100000) die('shit broken' . PHP_EOL);
}
printf('Arrived at node ZZZ! It took %d steps.' . PHP_EOL, $currentStep);

function getNextInstruction(string $instructions, int $currentStep): string
{
    //printf('getting next instruction from %s at step %d' . PHP_EOL, $instructions, $currentStep);
    while ($currentStep >= strlen($instructions)) {
        $currentStep -= strlen($instructions);
    }

    return substr($instructions, $currentStep, 1);
}*/

function parseNodes(array $lines): array
{
    $nodes = [];
    for ($i = 0; $i < count($lines); $i++) {
        [$node, $nextNodes] = explode(' = ', $lines[$i]);
        $nodes[$node] = [
            'L' => substr($nextNodes, 1, 3),
            'R' => substr($nextNodes, 6, 3),
        ];
    }

    return $nodes;
}


function dd($a, $b = null, $c = null, $d = null): void
{
    die(var_dump($a, $b, $c, $d));
}