Leetcode 105. Construct Binary Tree from Preorder and Inorder Traversal

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

Medium

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

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

For example, given

preorder = [3,9,20,15,7]
inorder = [9,3,15,20,7]

Return the following binary tree:

    3
   / \
  9  20
    /  \
   15   7

---

• 分治。先在前序里找到根结点，然后把中序分成左右子树分治。
• https://leetcode.com/problems/construct-binary-tree-from-preorder-and-inorder-traversal/discuss/34579/Python-short-recursive-solution.
• 5. Data Structures — Python 3.7.4 documentation
  • https://docs.python.org/3/tutorial/datastructures.html?highlight=list%20pop#more-on-lists

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution:
    def buildTree(self, preorder: List[int], inorder: List[int]) -> TreeNode:
        idx = inorder.index( preorder.pop( 0 ) )
        
        node = TreeNode( inorder[ idx ] )
        
        node.left = buildTree( preorder, inorder[ 0:idx ] )
        node.right = buildTree( preorder, inorder[ idx+1: ] )
        
        return node