# -*- coding: utf-8 -*-

class Solution:

def __init__(self):

self.ret = []

"""

@param root: The root of binary tree.

@return: Preorder in ArrayList which contains node values.

"""

def preorderTraversal(self, root):

# write your code here

if root is not None:

self.ret.append(root.val)

self.preorderTraversal(root.left)

self.preorderTraversal(root.right)

return self.ret