栈和队列_leetcode144

# Definition for a binary tree node.
# class TreeNode(object):
# def __init__(self,x):
# self.val = x
# self.left = None
# self.right = None

class Solution(object):
def preorderTraversal(self,root):
"""
 :type root: TreeNode
 :rtype: List[int]
 """

 res = []
self.order(root,res)
return res

def order(self,root,res):

if root:
 res.append(root.val)

self.order(root.left,res)
self.order(root.right,res)