Online PHP editor | output for 7GOk3

<?php function buildRegexFrom(string $word): string { // Split word to letters $letters = str_split($word); // Creating all side of alternations in our regex foreach ($letters as $key => $letter) if (end($letters) != $letter) $regex[] = "$letter(?={$letters[$key + 1]})|(?<=$letter){$letters[$key + 1]}"; // Return whole cooked pattern return "~(?|((?>".implode('|', $regex).")+)|([$word]))~i"; } function longestSubstring(array $array, string $regex): array { foreach ($array as $value) { preg_match_all($regex, $value, $matches); usort($matches[1], function($a, $b) { return strlen($b) <=> strlen($a); }); // Store longest match being sorted $substrings[] = $matches[1][0]; } return $substrings; } print_r(longestSubstring(['Mymaxmuis', 'axmuis', 'muster'], buildRegexFrom('maxmuster')));