note

Author: guangxush

guangxu/202102/20210201.md

@@ -37,19 +37,17 @@ Return the following binary tree:
  */
 class Solution {
     public TreeNode buildTree(int[] preorder, int[] inorder) {
-       if(preorder==null||inorder==null||preorder.length==0||inorder.length==0){
-            return null;
-        }
-        TreeNode treeNode = new TreeNode(preorder[0]);
-        for(int i=0;i<inorder.length;i++){
-            if(inorder[i]==preorder[0]){
-                treeNode.left = buildTree(Arrays.copyOfRange(preorder, 1 ,i+1),
-                                         Arrays.copyOfRange(inorder, 0 ,i));
-                treeNode.right = buildTree(Arrays.copyOfRange(preorder, i+1 ,preorder.length),
-                                         Arrays.copyOfRange(inorder, i+1 ,inorder.length));
-            }
-        }
-        return treeNode;
+       if(preorder==null || inorder==null || preorder.length==0 || inorder.length==0){
+           return null;
+       }
+       TreeNode root = new TreeNode(preorder[0]);
+       for(int i=0;i<inorder.length;i++){
+           if(inorder[i]==preorder[0]){
+               root.left = buildTree(Arrays.copyOfRange(preorder, 1, i+1), Arrays.copyOfRange(inorder, 0, i));
+               root.right = buildTree(Arrays.copyOfRange(preorder, i+1, preorder.length), Arrays.copyOfRange(inorder, i+1, inorder.length));
+           }
+       }
+        return root;
     }
 }
 ```

guangxu/202102/20210202.md

@@ -1,15 +1,60 @@
 ## Algorithm
 
+[106. Construct Binary Tree from Inorder and Postorder Traversal](https://leetcode.com/problems/construct-binary-tree-from-inorder-and-postorder-traversal/)
 
-Construct Binary Tree from Inorder and Postorder Traversal    
+### Description
 
+Given inorder and postorder traversal of a tree, construct the binary tree.
 
-### Description
+Note:
+You may assume that duplicates do not exist in the tree.
+
+For example, given
+
+```
+inorder = [9,3,15,20,7]
+postorder = [9,15,7,20,3]
+```
+
+Return the following binary tree:
+
+```
+    3
+   / \
+  9  20
+    /  \
+   15   7
+```
 
 ### Solution
 
 ```java
-
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode(int x) { val = x; }
+ * }
+ */
+class Solution {
+    public TreeNode buildTree(int[] inorder, int[] postorder) {
+        if(inorder==null||postorder==null||inorder.length==0||postorder.length==0){
+            return null;
+        }
+        TreeNode treeNode = new TreeNode(postorder[postorder.length-1]);
+        for(int i=0;i<inorder.length;i++){
+            if(inorder[i]==postorder[postorder.length-1]){
+                treeNode.left = buildTree(Arrays.copyOfRange(inorder, 0, i),
+                                         Arrays.copyOfRange(postorder, 0, i));
+                treeNode.right = buildTree(Arrays.copyOfRange(inorder, i+1, inorder.length),
+                                         Arrays.copyOfRange(postorder, i, inorder.length-1));
+            }
+        }
+        return treeNode;
+    }
+}
 ```
 
 ### Discuss

guangxu/README.md

@@ -1,5 +1,6 @@
 | 标题 | Algorithm | Review | Tip | Share|
 | :-----| :---- | :---- |  :---- |  :---- |
+| [20210202](./202102/20210202.md) |[106. Construct Binary Tree from Inorder and Postorder Traversal(中序和后序构造二叉树)](https://leetcode.com/problems/construct-binary-tree-from-inorder-and-postorder-traversal/)||||
 | [20210201](./202102/20210201.md) |[105. Construct Binary Tree from Preorder and Inorder Traversal(前序和中序构造二叉树)](https://leetcode.com/problems/construct-binary-tree-from-preorder-and-inorder-traversal/)||||
 | [20210131](./202101/20210131.md) |[145. Binary Tree Postorder Traversal(二叉树后序遍历)](https://leetcode.com/problems/binary-tree-postorder-traversal/)||||
 | [20210130](./202101/20210130.md) |[144. Binary Tree Preorder Traversal(二叉树前序遍历)](https://leetcode.com/problems/binary-tree-preorder-traversal/)||||