Online PHP editor | output for lOZVQ

<?php function isPalindrome(string &$str): bool { $regex = <<<REGEX / ^ #start of string ( #start capture group 1 ( #start capture group 2 . #match any non-newline character ) #end capture group2 (?1) #repeat the expression of capture group 1 \2 #match the character from capture group 2 | #or .? #the middle character (if odd length input string) or no character (if even length input string) ) #end capture group 1 $ #end of string /x REGEX; return (bool) preg_match($regex, $str); } function sanitizePalindrome(&$str) { return preg_replace('/[^a-z]+/', '', strtolower($str)); } $tests = [ '', 'radar', 'f', 'neveroddoreven', 'foo', 'palindrome', 'Red rum, sir, is murder' ]; foreach ($tests as $test) { $test = sanitizePalindrome($test); // this is optional printf("%20s : %s\n", $test, json_encode(isPalindrome($test))); }