# 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 printFromTopToBottom(self, root):
        """
        :type root: TreeNode
        :rtype: List[List[int]]
        """
        def dfs(root, depth, res):
            if not root:
                return 
            if depth == len(res):
                res.append([])
            if depth % 2 == 1:
                res[depth].insert(0, root.val)
            else:
                res[depth].append(root.val)
            dfs(root.left, depth+1, res)
            dfs(root.right, depth+1, res)

        if not root:
            return []
        res = [[]]
        dfs(root, 0, res)
        return res