index.php

<?php
$input = array(
	"taco cat",
	"madam",
	"racecar",
	"A man, a plan, a canal, Panama!",
	"Palindrome",
	"Was it a car or a cat I saw?",
	"No 'x' in Nixon",
	"Coding Horror",
);

function sanitize($item) {
	$pattern = "/[^a-zA-Z0-9]/";
	return strtolower(preg_replace($pattern, "", $item));
};

function isPalindrome($item) {
	$item = sanitize($item);

	for ($i = 0; $i < strlen($item)/2; $i++) {
		$j = strlen($item) - $i - 1;
		if ($item[$j] !== $item[$i]) {
			return false;
		}
	}

	return true;
};

$output = array_filter($input, "isPalindrome");
print_r($output)
?>