32扩展. 把二叉树打印成n行

• tobeprint记录该层节点还有多少要打印的，当tobeprint == 0 时，该层打印完毕

# -*- 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
        if not pRoot:return ''
        queue = [pRoot]
        helper = []
        tobeprint = 1
        nextlevel = 0
        res = []
        while queue:
            if queue[0].left:
                queue.append(queue[0].left)
                nextlevel += 1
            if queue[0].right:
                queue.append(queue[0].right)
                nextlevel += 1
            tobeprint -= 1
            helper.append(queue[0].val)
            queue.pop(0)
            if tobeprint == 0:
                res.append(helper)
                helper = []
                tobeprint = nextlevel
                nextlevel = 0
        return res