3v4l.org

run code in 300+ PHP versions simultaneously
<?php $string = 'abclkjabc'; $notRepeated = []; foreach (count_chars($string, 1) as $char => $count) { if ($count === 1) { $notRepeated[] = chr($char); } } var_export($notRepeated); echo "\nCount = " . count($notRepeated);
Output for 7.4.0 - 7.4.33, 8.0.1 - 8.0.30, 8.1.0 - 8.1.34, 8.2.0 - 8.2.30, 8.3.0 - 8.3.30, 8.4.1 - 8.4.18, 8.5.0 - 8.5.3
array ( 0 => 'j', 1 => 'k', 2 => 'l', ) Count = 3

preferences:
71.11 ms | 1248 KiB | 4 Q