栈和队列_leetcode144-二叉树前序遍历非递归

# 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]
 """

 class Command(object):
 def __init__(self,com,node):
 self.com = com
 self.node = node


 res = []
 stack = []

 if not root:
 return res
 stack.append(Command("go",root))

 while stack:
 com = stack.pop()

 if com.com == "print":
 res.append(com.node.val)
 else:
 if com.node.right:
 stack.append(Command("go",com.node.right))
 if com.node.left:
 stack.append(Command("go",com.node.left))
 stack.append(Command("print",com.node))

 return res