note

Author: guangxush

guangxu/202209/20220920.md

@@ -1,11 +1,66 @@
 ## Algorithm
 
+[106. Construct Binary Tree from Inorder and Postorder Traversal](https://leetcode.com/problems/construct-binary-tree-from-inorder-and-postorder-traversal/)
+
 ### Description
 
-### Solution
+Given two integer arrays inorder and postorder where inorder is the inorder traversal of a binary tree and postorder is the postorder traversal of the same tree, construct and return the binary tree.
+
+Example 1:
+
+![](assets/20220920-e354285b.png)
+
+```
+Input: inorder = [9,3,15,20,7], postorder = [9,15,7,20,3]
+Output: [3,9,20,null,null,15,7]
+```
 
-```java 
+Example 2:
+
+```
+Input: inorder = [-1], postorder = [-1]
+Output: [-1]
+```
+
+Constraints:
+
+- 1 <= inorder.length <= 3000
+- postorder.length == inorder.length
+- -3000 <= inorder[i], postorder[i] <= 3000
+- inorder and postorder consist of unique values.
+- Each value of postorder also appears in inorder.
+- inorder is guaranteed to be the inorder traversal of the tree.
+- postorder is guaranteed to be the postorder traversal of the tree.
+
+### 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, postorder.length-1));
+            }
+        }
+        return treeNode;
+    }
+}
 ```
 
 ### Discuss

guangxu/202209/assets/20220920-e354285b.png

@@ -1,5 +1,6 @@
 | 标题 | Algorithm | Review | Tip | Share|
 | - | - | - | - | - |
+| [20220920](./202209/20220920.md) |[106. Construct Binary Tree from Inorder and Postorder Traversal(根据中序和后序遍历构造二叉树)](https://leetcode.com/problems/construct-binary-tree-from-inorder-and-postorder-traversal/)||||
 | [20220919](./202209/20220919.md) |[105. Construct Binary Tree from Preorder and Inorder Traversal(根据前序和中序构建二叉树)](https://leetcode.com/problems/construct-binary-tree-from-preorder-and-inorder-traversal/)||||
 | [20220918](./202209/20220918.md) |[116. Populating Next Right Pointers in Each Node(完美二叉树的每个节点增加Next指针)](https://leetcode.com/problems/populating-next-right-pointers-in-each-node/)||||
 | [20220917](./202209/20220917.md) |[117. Populating Next Right Pointers in Each Node II(完美二叉树的每个节点增加Next指针2)](https://leetcode.com/problems/populating-next-right-pointers-in-each-node-ii/)||||