Missing cards in deck

deck.php

<?php

function findMissingCards($deck)
{
	// The order is not the actual order of the cards in the deck, but the alpha order
	// because I didn't implement the sort method here, but used a native one
	$colors = array('C', 'P', 'Q', 'T');
	$values = array(2, 3, 4, 5, 6, 7, 8, 9, 10, 'V', 'D', 'R', 'A');
	$missingCards = array();

	if (is_string($deck)) {
		$deck = explode(' ', $deck);
	}
	else if (!is_array($deck)) {
		throw new InvalidArgumentException("invalid deck value");
	}
	$deck = array_flip($deck);

	foreach ($colors as $color) {
		foreach ($values as $value) {
			if (!isset($deck[$color . $value])) {
				$missingCards[] = $color . $value;
			}
		}
	}

	// custom sort to do
	sort($missingCards);

	return $missingCards;
}


$deck = array(
	"C2", "C3", "C4", "C8", "C9", "CV", "CD", "CR", "CA",
	"P2", "P3", "P4", "P5", "P6", "P8", "P9","PV", "PD", "PR", "PA",
	"Q2", "Q3", "Q4", "Q5", "Q6", "Q7", "Q8", "QV", "QD", "QR", "QA",
	"T2", "T3", "T9", "T10", "TV", "TD", "TR", "TA"
);

$missing = findMissingCards($deck);
var_dump(count($missing), count($deck), count($missing) + count($deck));