solution.py

from typing import List
from typing import Optional
# Definition for a binary tree node.


class TreeNode:
    def __init__(self, val=0, left=None, right=None):
        self.val = val
        self.left = left
        self.right = right


class Solution:
    def buildTree(self, preorder: List[int], inorder: List[int]) -> Optional[TreeNode]:
        if not preorder or not inorder:
            return None
        root = TreeNode(preorder[0])
        mid = inorder.index(preorder[0])
        root.left = self.buildTree(preorder[1:mid+1], inorder[:mid])
        root.right = self.buildTree(preorder[mid+1:], inorder[mid+1:])
        return root


if __name__ == '__main__':
    preorder = [3, 9, 20, 15, 7]
    inorder = [9, 3, 15, 20, 7]
    print(Solution().buildTree(preorder, inorder))