实现二叉树先序、中序、后序遍历

实现二叉树先序，中序和后序遍历_牛客题霸_牛客网

问题简述

给定一棵二叉树，分别按照二叉树先序，中序和后序打印所有的节点。

思路：DFS

Python

# 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
        
        p, i, s = [], [], []
        
        def dfs(x):
            if x is None:
                return 
            
            p.append(x.val)
            dfs(x.left)
            i.append(x.val)
            dfs(x.right)
            s.append(x.val)
        
        dfs(root)
        return [p, i, s]