奇怪的洗牌逻辑

class demo
{
    private $dic = array('a', 'b', 'c', 'd'); // 花色

    private $kings = array('w1', 'w2'); // 大小王

    private $card_set = array(); // 扑克牌

    private $card_array = array(); // 洗好的牌


    // 执行随机洗牌
    public function getCardSet()
    {
        $this->createCard();

        for($i = 0; $i < 54; $i++)
        {
            $this->getRandNum();

            $k = $this->key;

            $this->card_array[$i] = $this->card_set[$k];

            unset($this->card_set[$k]);
        }

        ksort($this->card_array);

        return implode(',', $this->card_array);
    }

    // 生成扑克牌
    public function createCard()
    {
        $tmp_card = array();

        for($i = 1; $i <= 13; $i++)
        {
            $count = count($this->dic);

            for($j = 0; $j < $count; $j++)
            {
                $tmp_card[] = $this->dic[$j] . $i;
            }
        }

        $this->card_set = array_merge($tmp_card, $this->kings);
    }

    // 生成随机数
    public function getRandNum()
    {
        $num = microtime(true);
        $k = rand(0, 53);
        if(! isset($this->card_set[$k]))
        {
            $this->getRandNum();
        }
        else
        {
            $this->key = $k;
        }
    }
}