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
        pre_list = []
        in_list = []
        post_list = []

        def preorder(leaf: TreeNode):
            if not leaf:
                return
            pre_list.append(leaf.val)
            preorder(leaf.left)
            preorder(leaf.right)

        def inorder(leaf: TreeNode):
            if not leaf:
                return
            inorder(leaf.left)
            in_list.append(leaf.val)
            inorder(leaf.right)

        def postorder(leaf: TreeNode):
            if not leaf:
                return
            postorder(leaf.left)
            postorder(leaf.right)
            post_list.append(leaf.val)

        preorder(root)
        inorder(root)
        postorder(root)
        result = []
        result.append(pre_list)
        result.append(in_list)
        result.append(post_list)
        return result