PHP – VDonC#ev

Look And Say Sequence – PHP 7.4

<?php

$num = "011223333";
$res = preg_replace_callback(
    '/(\d)\1*/', fn($match) => strlen($match[0]) . $match[0][0], $num
);

var_dump($res); //102243

Look and Say Sequence in PHP

<?php

echo implode("<br>", lookAndSay(0, 5));

function lookAndSay(string $num, int $count): array
{
    $results = [$num];

    for ($i = 0; $i < $count; $i++) {
        preg_match_all('/(\d)\1*/', $num, $matches);

        $num = implode('',
            array_map(function ($item) {
                return strlen($item) . $item[0];
            }, $matches[0]));

        $results[] = $num;
    }

    return $results;
}