题目：
题解：
class Solution:def levelOrderBottom(self, root: TreeNode) -> List[List[int]]:levelOrder = list()if not root:return levelOrderq = collections.deque([root])while q:level = list()size = len(q)for _ in range(size):node = q.popleft()level.append(node.val)if node.left:q.append(node.left)if node.right:q.append(node.right)levelOrder.append(level)return levelOrder[::-1]
