数据结构（树）

 static void SwapNode(Node node)
        {
            if (node == null)
            {
                return;
            }

            Node temp = node.Left;

            node.Left = node.Right;
            node.Right = temp;

            SwapNode(node.Left);
            SwapNode(node.Right);
        }

    static void PrintFromTopToBottom(Node node)
        {
            if (node == null)
            {
                return;
            }
            Queue<Node> queue = new Queue<Node>();
            queue.Enqueue(node);
            while (queue.Count > 0)
            {
                Node current = queue.Dequeue();
                Console.WriteLine(current.Value);
                if (current.Left != null)
                {
                    queue.Enqueue(current.Left);
                }
                if (current.Right != null)
                {
                    queue.Enqueue(current.Right);
                }
            }
        }