using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;namespace ConsoleApplication5{ class Program {  static void Main(string[] args)  {   Node treeRoot = CreateTree();   scanTree(treeRoot);  }  private static void scanTree(Node treeRoot)  {   List<Node> list = new List<Node>();   list.Add(treeRoot);   Node point = treeRoot;   Write(treeRoot);   while (true)   {    if (!list.Contains(point))    { //上一輪是移除的操作     if (treeRoot.leftSon == point)     {//移除的是左結點      if (treeRoot.rightSon != null)      {       treeRoot = treeRoot.rightSon;       list.Add(treeRoot);       Write(treeRoot);       point = treeRoot;       continue;      }      list.Remove(treeRoot);      if (list.Count == 0)      {       break;      }      point = treeRoot;      treeRoot = list[list.Count - 1];     }     else     {//移除的是右結點      list.Remove(treeRoot);      if (list.Count == 0)      {       break;      }      point = treeRoot;      treeRoot = list[list.Count - 1];     }     continue;    }    if (treeRoot.leftSon != null)    {     treeRoot = treeRoot.leftSon;     Write(treeRoot);     list.Add(treeRoot);     point = treeRoot;     continue;    }    if (treeRoot.rightSon != null)    {     treeRoot = treeRoot.rightSon;     Write(treeRoot);     point = treeRoot;     list.Add(treeRoot);     continue;    }    if (treeRoot.leftSon == null && treeRoot.rightSon == null)    {     list.Remove(treeRoot);     if (list.Count == 0)     {      break;     }     point = treeRoot;     treeRoot = list[list.Count - 1];    }   }  }  public static void Write(Node node)  {   Console.WriteLine(node.Data);  }  private static Node CreateTree()  {   Node a = new Node("A");   a.leftSon = new Node("B");   a.rightSon = new Node("C");   a.leftSon.leftSon = new Node("D");   a.leftSon.rightSon = new Node("E");   a.rightSon.leftSon = new Node("F");   a.rightSon.rightSon = new Node("G");   a.leftSon.leftSon.leftSon = new Node("H");   a.leftSon.leftSon.rightSon = new Node("I");   return a;  } } class Node {  public string Data { get; set; }  public Node leftSon { get; set; }  public Node rightSon { get; set; }  public Node(string data)  {   Data = data;  } }}