# 106. Construct Binary Tree from Inorder and Postorder Traversal

#### Medium

***

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:**

![](https://assets.leetcode.com/uploads/2021/02/19/tree.jpg)

```
Input: inorder = [9,3,15,20,7], postorder = [9,15,7,20,3]
Output: [3,9,20,null,null,15,7]
```

**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.

```python
class Solution:
    def buildTree(self, inorder: List[int], postorder: List[int]) -> Optional[TreeNode]:
        if inorder:
            index = inorder.index(postorder.pop())
            root = TreeNode(inorder[index])
            root.right = self.buildTree(inorder[index+1:], postorder)
            root.left = self.buildTree(inorder[:index],  postorder)
            return root
```