preorder tree using stack

Author: jackzhenguo

Tree/Tree.TreeLib/PreOrderStack.cs

@@ -0,0 +1,59 @@
+/* ==============================================================================
+ * 功能描述：PreorderStack  
+ * 创 建 者：gz
+ * 创建日期：2017/5/12 15:06:49
+ * ==============================================================================*/
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Windows.Forms;
+using System.Windows.Forms.VisualStyles;
+
+//Given a binary tree, return the inorder traversal of its nodes' values.
+
+//For example:
+//Given binary tree [1,null,2,3],
+//   1
+//    \
+//     2
+//    /
+//   3
+//return [1,3,2].
+
+//Note: Recursive solution is trivial, could you do it iteratively?
+namespace InorderTreeStackSln
+{
+
+
+    /// <summary>
+    /// InorderStack
+    /// </summary>
+    public class PreorderStack
+    {
+        public IList<int> PreorderTraversal(TreeNode root)
+        {
+            IList<int> rtn = new List<int>();
+            if (root == null) return rtn;
+
+            Stack<TreeNode> s = new Stack<TreeNode>();
+            s.Push(root);
+            TreeNode tmp = root;
+            while (s.Count > 0)
+            {
+                if (tmp == null)
+                    tmp = s.Peek(); 
+                rtn.Add(s.Peek().val);
+                s.Pop();
+                if(tmp.right!=null)
+                   s.Push(tmp.right);
+                if (tmp.left != null)
+                    s.Push(tmp.left);
+                tmp = tmp.left;
+            }
+            return rtn;
+        }
+    }
+
+
+}