题解 | #实现二叉树先序，中序和后序遍历#

# class TreeNode:
#     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 root TreeNode类 the root of binary tree
# @return int整型二维数组
#
class Solution:
    def threeOrders(self , root: TreeNode) -> List[List[int]]:
        # write code here
        if not root:
            return [[],[],[]]
        elif root.left==root.right==None:
            return [[root.val],[root.val],[root.val]]

        first=[root.val]+self.threeOrders(root.left)[0]+self.threeOrders(root.right)[0]
        mid=self.threeOrders(root.left)[1]+[root.val]+self.threeOrders(root.right)[1]
        last=self.threeOrders(root.left)[2]+self.threeOrders(root.right)[2]+[root.val]

        return [first,mid,last]