#!/usr/bin/env python3
# -*- coding: utf-8 -*-
# author: bt3gl
# 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.


def fill_tree(i_left, i_right, inorder_map):
            
        if i_left > i_right:
                return None
            
        val = postorder.pop()
        root = TreeNode(val)

        index_here = inorder_map[val]

        root.right = fill_tree(index_here + 1, i_right, inorder_map)
        root.left = fill_tree(i_left, index_here - 1, inorder_map)
            
        return root


def build_tree(inorder: list[int], postorder: list[int]) -> Optional[TreeNode]:

        inorder_map = {val: index for index, val in enumerate(inorder)}
        return fill_tree(0, len(inorder) - 1, inorder_map)