LeetCode105_从前序与中序遍历序列构造二叉树

1. 题目

给定两个整数数组 preorder 和 inorder ，其中 preorder 是二叉树的先序遍历， inorder 是同一棵树的中序遍历，请构造二叉树并返回其根节点。      

2. 题解

from typing import List


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]) -> TreeNode:
        if not preorder and not inorder:
            return None
        root = TreeNode(preorder[0])
        i = inorder.index(preorder[0])

        root.left = self.buildTree(preorder[1: i+1], inorder[: i])
        root.right = self.buildTree(preorder[i + 1:], inorder[i + 1:])
        return root


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