从上往下打印二叉树

题目描述
从上往下打印出二叉树的每个节点，同层节点从左至右打印。

python solution:

# -*- coding:utf-8 -*-
class TreeNode:
    def __init__(self, x):
        self.val = x
        self.left = None
        self.right = None

class Solution:
    # 返回从上到下每个节点值列表，例：[1,2,3]
    def PrintFromTopToBottom(self, root):
        l,res = [],[]
        if root is None:
            return res
        l.append(root)
        while len(l):
            temp = l.pop(0)
            res.append(temp.val)
            if temp.left:
                l.append(temp.left)
            if temp.right:
                l.append(temp.right)
        return res