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
        ans = [[],[],[]]
        if not root:
            return ans
        def firstOrder(root):
            ans[0].append(root.val)
            if root.left:
                firstOrder(root.left)
            if root.right:
                firstOrder(root.right)
        
        def midOrder(root):
            if root.left:
                midOrder(root.left)
            ans[1].append(root.val)
            if root.right:
                midOrder(root.right)
        
        def postOrder(root):
            if root.left:
                postOrder(root.left)
            if root.right:
                postOrder(root.right)
            ans[2].append(root.val)
        firstOrder(root)
        midOrder(root)
        postOrder(root)
        return ans