LeetCode105_從前序與中序周遊序列構造二叉樹

1. 題目

給定兩個整數數組 preorder 和 inorder ，其中 preorder 是二叉樹的先序周遊， inorder 是同一棵樹的中序周遊，請構造二叉樹并傳回其根節點。      

2. 題解

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)