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)