题解 | #重建二叉树#

#递归方法

#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None
#
# 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
#
# 
# @param pre int整型一维数组 
# @param vin int整型一维数组 
# @return TreeNode类
#
class Solution:
    def reConstructBinaryTree(self , pre: List[int], vin: List[int]) -> TreeNode:
        if pre == []:
            return None
        #设定根节点
        root = TreeNode(pre[0])
        #找到根节点在中序对应的索引，对应出左子树和右子树
        in_index = vin.index(root.val)
        in_left = vin[:in_index]
        #根据左右子树序列长度，确定先序序列中的左子树和右子树
        len_left = len(in_left)
        in_right = vin[in_index+1:]
        pre_left = pre[1:len_left+1]
        pre_right = pre[len_left+1:]
        root.left = self.reConstructBinaryTree(pre_left, in_left)
        root.right = self.reConstructBinaryTree(pre_right, in_right)
        return root