JZ78 把二叉树打印成多行

class Solution:
    # 返回二维列表[[1,2],[4,5]]
    def Print(self, pRoot):
        # write code here
        if pRoot is None:
            return []
        current = []
        current.append(pRoot)
        next_layer = []
        result = []
        while current:
            for node in current:
                if node.left:
                    next_layer.append(node.left)
                if node.right:
                    next_layer.append(node.right)
            result.append([i.val for i in current])
            current, next_layer = next_layer, []
        return result