很显然，这与前面的一题的本质区别是，不再是简单的追加。要区分追加的分类。
# Definition for a binary tree node. # class TreeNode: # def __init__(self, x): # self.val = x # self.left = None # self.right = None class Solution: def levelOrder(self, root: TreeNode) -> List[List[int]]: if not root: return [] res, queue = [], collections.deque() queue.append(root) while queue: tmp = [] for _ in range(len(queue)): node = queue.popleft() tmp.append(node.val) if node.left: queue.append(node.left) if node.right: queue.append(node.right) res.append(tmp) return res
# Definition for a binary tree node. # class TreeNode: # def __init__(self, x): # self.val = x # self.left = None # self.right = None class Solution: def levelOrder(self, root: TreeNode) -> List[List[int]]: if not root: return [] res, queue = [],[root] while queue: tmp=[] for _ in range(len(queue)): node = queue.pop(0) tmp.append(node.val) if node.left: queue.append(node.left) if node.right: queue.append(node.right) res.append(tmp) return res
原文：https://www.cnblogs.com/topass123/p/12764556.html