二叉树的前序中序后序遍历-非递归-使用同一段代码实现

 1     class TreeNodeWithIndex{
 2         public TreeNode node;
 3         public int index=0;
 4         public TreeNodeWithIndex(TreeNode n) { node = n; }
 5     }
　　　　//0 pre ; 1 inorder ; 2 post 
 6     public IList<int> TreeTraversal(TreeNode root,int type)
 7     {
 8         var stack = new Stack<TreeNodeWithIndex>();
 9         var ans = new List<int>();
10         stack.Push(new TreeNodeWithIndex(root));
11         while (stack.Count!=0)
12         {
13             var i = stack.Peek();
14             if (i.index > 2 || i.node == null) { stack.Pop(); continue; }
15             if (type == i.index) ans.Add(i.node.val);
16             else
17             {
18                 int tmp = type - i.index * 2;
19                 if (tmp > 0 || tmp == -2)
20                     stack.Push(new TreeNodeWithIndex(i.node.left));
21                 else
22                     stack.Push(new TreeNodeWithIndex(i.node.right));
23             }
24             i.index++;
25         }
26         return ans;
27     }