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