Advent of Code - day 9

day9.php

<?php
declare(strict_types=1);

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

$totalNextNumbers = 0;
$totalPreviousNumbers = 0;
foreach ($input as $line) {
    $numbers = explode(' ', $line);
    [$nextNumber, $previousNumber] = findNextAndPreviousNumber($numbers);
    printf('Next line in number sequence "%s" is: %s' . PHP_EOL, $line, $nextNumber);
    printf('...and the previous number is: %s' . PHP_EOL, $previousNumber);
    $totalNextNumbers += $nextNumber;
    $totalPreviousNumbers += $previousNumber;
}
printf('Total difference for next numbers: %s' . PHP_EOL, $totalNextNumbers);
printf('Total different for previous numbers: %s' . PHP_EOL, $totalPreviousNumbers);

function findNextAndPreviousNumber(array $numbers): array
{
    $numbersList = [];
    while (areAllSameNumbers($numbers) === false) {
        $numbersList[] = $numbers;
        $numbers = findDifferences($numbers);
    }

    $nextNumber = $numbers[0];
    $previousNumber = $numbers[0];
    foreach (array_reverse($numbersList) as $list) {
        $nextNumber = end($list) + $nextNumber;
        $previousNumber = reset($list) - $previousNumber;
    }

    return [$nextNumber, $previousNumber];
}

function findDifferences(array $numbers): array
{
    $newNumbers = [];
    for ($i = 1; $i < count($numbers); $i++) {
        $newNumbers[] = $numbers[$i] - $numbers[$i - 1];
    }

    return $newNumbers;
}

function areAllSameNumbers(array $numbers): bool
{
    return implode('', $numbers) === str_repeat((string)$numbers[0], count($numbers));
}

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