add traversal btree stack version

Author: jackzhenguo

Tree/Tree.TreeLib/TraversalTreeUsingStack.cs

@@ -0,0 +1,97 @@
+/* ==============================================================================
+ * 功能描述：TraversalTreeUsingStack  
+ * 创 建 者：gz
+ * 创建日期：2017/4/24 10:39:19
+ * ==============================================================================*/
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+
+namespace Tree.TreeLib
+{
+    /// <summary>
+    /// TraversalTreeUsingStack
+    /// </summary>
+    public class TraversalTreeUsingStack
+    {
+        private Stack<TreeNode> _stack = new Stack<TreeNode>();
+        //前序遍历
+        public void PreOrder(TreeNode root)
+        {
+            _stack.Clear();
+            if (root == null)
+                return;
+            TreeNode tmp = root;
+            _stack.Push(tmp);//先访问根节点
+            while (_stack.Count > 0)
+            {
+                if (tmp == null)//左子树为空             
+                    tmp = _stack.Peek(); //弹出右子树
+                visit(_stack.Peek());
+                _stack.Pop();
+                if (tmp.right != null)
+                    _stack.Push(tmp.right);
+                if (tmp.left != null)
+                    _stack.Push(tmp.left);
+                tmp = tmp.left;//迭代等式
+            }
+        }
+        //中序遍历
+        //先遍历左孩子，再访问根节点，最后遍历右孩子
+        public void MidOrder(TreeNode root)
+        {
+            _stack.Clear();
+            if (root == null) return;
+            _stack.Push(root);
+            while (_stack.Count > 0)
+            {
+                TreeNode tmp = _stack.Peek();
+                while (tmp != null) //遍历左子树的最孩子，直到为null
+                {
+                    _stack.Push(tmp.left);
+                    tmp = tmp.left;
+                }
+                //可能1 左孩子为null时退出上层循环，但是此时栈顶为null
+                //可能2 栈顶为null，while直接退出
+                _stack.Pop(); //一定弹出null       
+                if (_stack.Count == 0) return;
+                visit(_stack.Peek()); //访问节点    
+                var tmp2 = _stack.Pop();
+                _stack.Push(tmp2.right);//如果右孩子为null，则null入栈。
+            }
+        }
+
+        //后序遍历
+        public void PostOrder(TreeNode root)
+        {
+            _stack.Clear();
+            if (root == null) return;
+            _stack.Push(root);
+            TreeNode tmp = root;
+            while (_stack.Count > 0)
+            {
+                if (tmp == null)
+                {
+                    _stack.Pop();
+                    tmp = _stack.Peek();
+                    continue;
+                }
+                if (tmp.right != null)
+                    _stack.Push(tmp.right);
+                if (tmp.left != null)
+                    _stack.Push(tmp.left);
+                visit(_stack.Peek());
+                tmp = _stack.Pop();
+            }
+        }
+
+
+        private void visit(TreeNode node)
+        {
+            if (node != null)
+                Console.WriteLine(node.val);
+        }
+
+    }
+}