aoc2017/day6/main.php

<?php
// https://adventofcode.com/2017/day/6

function puzzle1(string $input) : int
{
    $history = [];
    $banks = explode("\t", $input);
    $sum = 0;

    while (true) {
        // Copy banks, sort it, get biggest number out
        $copy = $banks;
        rsort($copy);
        $biggestNumber = array_shift($copy);

        // Find the key and value to distribute
        $distributeKey = array_search($biggestNumber, $banks);
        $distributeValue = $banks[$distributeKey];
        $banks[$distributeKey] = 0;

        while ($distributeValue > 0) {
            $distributeKey++;

            if ($distributeKey > count($banks) - 1) {
                $distributeKey = 0;
            }

            $banks[$distributeKey]++;

            $distributeValue--;
        }

        // Increment reallocations
        $sum++;

        // Check history if we had this state before
        $index = implode($banks, '');

        if (isset($history[$index])) {
            break;
        }

        $history[$index] = true;
    }

    return $sum;
}

function puzzle2(string $input) : int
{
    $history = [];
    $banks = explode("\t", $input);
    $sum = 0;

    while (true) {
        // Copy banks, sort it, get biggest number out
        $copy = $banks;
        rsort($copy);
        $biggestNumber = array_shift($copy);

        // Find the key and value to distribute
        $distributeKey = array_search($biggestNumber, $banks);
        $distributeValue = $banks[$distributeKey];
        $banks[$distributeKey] = 0;

        while ($distributeValue > 0) {
            $distributeKey++;

            if ($distributeKey > count($banks) - 1) {
                $distributeKey = 0;
            }

            $banks[$distributeKey]++;

            $distributeValue--;
        }

        // Increment reallocations
        $sum++;

        // Check history if we had this state before
        $index = implode($banks, '');

        if (isset($history[$index])) {
            $sum = $sum - $history[$index];
            break;
        }

        $history[$index] = $sum;
    }

    return $sum;
}

echo 'First challange solution:'.PHP_EOL;
echo puzzle1(trim(file_get_contents(dirname(__FILE__).'/input.txt'))).PHP_EOL;

echo 'Second challange solution:'.PHP_EOL;
echo puzzle2(trim(file_get_contents(dirname(__FILE__).'/input.txt'))).PHP_EOL;