剑指Offer60：把二叉树打印成多行

思路：

 数组初始化注意，有的需要在循环里面。刚开始需要判断pRoot是否为空。

# -*- coding:utf-8 -*-
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None
class Solution:
    # 返回二维列表[[1,2],[4,5]]
    def Print(self, pRoot):
        # write code here
        res = []
        if not pRoot:
            return res
        level = []
        level.append(pRoot)
        while level:
            res.append([node.val for node in level])
            next_level = []
            for node in level:
                if node.left:
                    next_level.append(node.left)
                if node.right:
                    next_level.append(node.right)
            level = next_level
        return res