Merge branch 'master' of github.com:jackzhenguo/leetcode-csharp

Author: jackzhenguo

README.md

@@ -3,17 +3,13 @@
 * CSDN Column(http://blog.csdn.net/column/details/14761.html) where detail solutions are.
 ## `Today Update`
 ### Tree
-####  103 Binary Tree Zigzag Level Order Traversal
-*  [Github:#103 Binary Tree Zigzag Level Order Traversal](/Tree/Tree.TreeLib/ZigzagLevelOrder.cs)
-*  [CSDN:#103 Binary Tree Zigzag Level Order Traversal](http://blog.csdn.net/daigualu/article/details/72039636)
- ####  95 Unique Binary Search Trees II
-*  [Github:#95 Unique Binary Search Trees II](/Tree/Tree.TreeLib/UniqueBSTSln.cs)
-*  [CSDN:#95 Unique Binary Search Trees II](http://blog.csdn.net/daigualu/article/details/72051612)
-   * this is the famous "Catalan number", please reference https://en.wikipedia.org/wiki/Catalan_number
-     * apply 1: valid stack oepration: ((ab)c)d     (a(bc))d     (ab)(cd)     a((bc)d)     a(b(cd))
-	 * apply 2: ![binary trees](/Tree/Tree.TreeLib/binarytrees.jpg)
-	 * apply 3: ![triangles](/Tree/Tree.TreeLib/triangles.jpg)
-	 * apply 4: ![stairs](/Tree/Tree.TreeLib/stairs.jpg)
+####  105 Construct Binary Tree from Preorder and Inorder Traversal
+*  [Github:#105 Construct Binary Tree from Preorder and Inorder Traversal](/Tree/Tree.TreeLib/BuildTreeByPreAndInorder.cs)
+*  [CSDN:#105 Construct Binary Tree from Preorder and Inorder Traversal](http://blog.csdn.net/daigualu/article/details/72127022)
+*  Tips:
+   * the most important function in solving this issue is 
+       *  private TreeNode bulidTree(int preStart, int inStart, int inEnd) ;
+   * Plus, preStart index in preorder is the root index, which is also the separate point in inorder and it’s left is left subtree and right is right subtree.
 ---
 ---
 
@@ -222,3 +218,14 @@ Tags are following:
 *  [Github:#572 Subtree of Another Tree](/Tree/Tree.TreeLib/IsSameTreeSln.cs)
 *  [CSDN:#572 Subtree of Another Tree](http://blog.csdn.net/daigualu/article/details/71908238)
    * Subtree of Another Tree: it's extended from problem of "is same tree".
+####  103 Binary Tree Zigzag Level Order Traversal
+*  [Github:#103 Binary Tree Zigzag Level Order Traversal](/Tree/Tree.TreeLib/ZigzagLevelOrder.cs)
+*  [CSDN:#103 Binary Tree Zigzag Level Order Traversal](http://blog.csdn.net/daigualu/article/details/72039636)
+ ####  95 Unique Binary Search Trees II
+*  [Github:#95 Unique Binary Search Trees II](/Tree/Tree.TreeLib/UniqueBSTSln.cs)
+*  [CSDN:#95 Unique Binary Search Trees II](http://blog.csdn.net/daigualu/article/details/72051612)
+   * this is the famous "Catalan number", please reference https://en.wikipedia.org/wiki/Catalan_number
+     * apply 1: valid stack oepration: ((ab)c)d     (a(bc))d     (ab)(cd)     a((bc)d)     a(b(cd))
+	 * apply 2: ![binary trees](/Tree/Tree.TreeLib/binarytrees.jpg)
+	 * apply 3: ![triangles](/Tree/Tree.TreeLib/triangles.jpg)
+	 * apply 4: ![stairs](/Tree/Tree.TreeLib/stairs.jpg)

Tree/Tree.TreeLib/BuildTreeByPreAndInorder.cs

@@ -0,0 +1,57 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+
+namespace Tree.TreeLib
+{
+    // // Given preorder and inorder traversal of a tree, construct the binary tree.
+
+// // Note: 
+// // You may assume that duplicates do not exist in the tree.
+   public class Solution 
+{
+    private  int[] _preorder; //preorder array
+    private  int[] _inorder; //inorder array
+    public TreeNode BuildTree(int[] preorder, int[] inorder)
+     {
+        _preorder = preorder;
+        _inorder = inorder;
+        //if(_preorder.Length==0 || inorder.Length==0) return null;
+        //if(prorder.Length!=inorder.Length) return null;
+        return bulidTree(0,0,_inorder.Length-1);
+    }
+    //preStart: index of root of tree
+    //inStart: of inorder tree, inStart ~ root index - 1 -> left tree
+    //EndStart:of inorder tree, root index + 1 ~ inEnd -> right tree
+    private TreeNode  bulidTree(int preStart, int inStart, int inEnd) 
+    {
+        if (preStart > _preorder.Length - 1 || inStart > inEnd)
+         {
+            return null;
+        }
+        TreeNode root = new TreeNode(_preorder[preStart]); 
+        // find the index of current root in inorder. 
+        int inIndex = curRootIndex(inStart, inEnd, root); 
+        root.left = bulidTree(preStart + 1, inStart, inIndex - 1);
+        //right subtree begins position in preorder
+        preStart += inIndex - inStart + 1; 
+        root.right = bulidTree(preStart, inIndex + 1, inEnd);
+        return root;
+    }
+
+      private int curRootIndex(int inStart, int inEnd, TreeNode root)
+      {
+           for (int i = inStart; i <= inEnd; i++) 
+           {
+               if (_inorder[i] == root.val) 
+                {
+                   return i;
+                }
+            }
+          return -1;
+        }
+
+  }
+
+}