题目：
题解：
class Solution:def levelOrder(self, root: 'Node') -> List[List[int]]:if not root:return []ans = list()q = deque([root])while q:cnt = len(q)level = list()for _ in range(cnt):cur = q.popleft()level.append(cur.val)for child in cur.children:q.append(child)ans.append(level)return ans
