advent_of_code_day_1.php

<?php

// https://adventofcode.com/2023/day/1/answer

$lines = file('data.txt');
$calibrationValues = getCalibrationValues($lines);
$sum = array_sum($calibrationValues);

/**
 * @return int[]
 */
function getCalibrationValues(array $lines): array
{
    return array_map(getCalibrationValue(...), $lines);
}

function getCalibrationValue(string $line): int
{
    $digits = getDigits(replaceTextualDigits($line));
    return $digits[0] * 10 + $digits[count($digits) - 1];
}

function replaceTextualDigits(string $line): string
{
    $textualDigits = [
        'zero',
        'one',
        'two',
        'three',
        'four',
        'five',
        'six',
        'seven',
        'eight',
        'nine',
    ];
    $digits = array_flip($textualDigits);
    $regex = '/' . join('|', $textualDigits) . '/';
    return preg_replace_callback(
        $regex,
        fn(array $matches) => $digits[$matches[0]],
        $line
    );
}

/**
 * @return int[]
 */
function getDigits(string $line): array
{
    return str_split(preg_replace('/[^\d]/', '', $line));
}