/**
     * 单链表反转
     * @param node 头结点
     * @return 翻转后的头结点，原链表尾节点
     */
    public static Node reverseList(Node node) {
        Node currNode = node;
        Node preNode = null;
        while (currNode != null) {
            Node nextNode = currNode.next;
            currNode.next = preNode;
            preNode = currNode;
            currNode = nextNode;
        }
        return preNode;
    }