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:

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.

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