https://leetcode.com/problems/construct-binary-tree-from-inorder-and-postorder-traversal/

reconstructBinaryTreeFromTwoTraversals.py

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None
# E.g., 
# [9, 15, 7, 20, 3] postorder
# [9, 3, 15, 20, 7] inorder
class Solution:
    def buildTree(self, inorder: List[int], postorder: List[int]) -> TreeNode:
        io = {value:index for index, value in enumerate(inorder)}
        
        def tree(ioLeft: int, ioRight: int) -> TreeNode:
            
            if ioLeft > ioRight: return None # no root available
            
            root = postorder.pop()
            rootNode = TreeNode(root)
            
            rootPos = io[root]
            rootNode.right = tree(rootPos+1, ioRight)
            rootNode.left  = tree(ioLeft, rootPos-1)
            
            return rootNode
            
        return tree(0, len(inorder)-1)