<?php function unique_chars(string $input, bool $multibyte = true): int { $chars = []; $strlen = $multibyte ? 'mb_strlen' : 'strlen'; $substr = $multibyte ? 'mb_substr' : 'substr'; $length = $strlen($input); for($i = 0; $i < $length; $i++) { $current = $substr($input, $i, 1); if(!in_array($current, $chars, true)) { $chars[] = $current; } } return count($chars); }