106 - Construct Binary Tree from Inorder and Postorder Traversal

2020/05/02

leetcode

Problem

Given inorder and postorder traversal of a tree, construct the binary tree.

Note:
You may assume that duplicates do not exist in the tree.

For example, given

inorder = [9,3,15,20,7]
postorder = [9,15,7,20,3]
Return the following binary tree:

    3
   / \
  9  20
    /  \
   15   7

Solution

The problem is almost the same as 105 Construct BT from Preorder and Inorder. Notes can be found there.

class Solution:
    def buildTree(self, inorder: List[int], postorder: List[int]) -> TreeNode:
        if inorder:
            node = TreeNode(postorder.pop())
            split = inorder.index(node.val)
            node.right = self.buildTree(inorder[split + 1:], postorder)
            node.left = self.buildTree(inorder[:split], postorder)

            return node