題目：

從上往下打印出二叉樹的每個節點，同層節點從左至右列印。

解答：

# -*- coding:utf-8 -*-
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None
import Queue
class Solution:
    # 返回從上到下每個節點值列表，例：[1,2,3]
    def PrintFromTopToBottom(self, root):
        # write code here
 

        rlist = []
        q = Queue.Queue()
        if root != None:
            q.put(root)
        while(not q.empty()):
            node = q.get()
            rlist.append(node.val)
            if node.left:
                q.put(node.left)
            if node.right:
                q.put(node.
 
right)
        return rlist