题目如下：

解题思路：凑数题+1，话说我这个也是凑数博？

代码如下：

class Solution(object):    def preorder(self, root):        """        :type root: Node        :rtype: List[int]        """        if root == None:            return []        res = []        stack = [root]        while len(stack) > 0:            node = stack.pop(0)            res.append(node.val)            for i in node.children[::-1]:                stack.insert(0,i)        return res