Solution.py

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution:
    def levelOrderBottom(self, root: TreeNode) -> List[List[int]]:
        if root is None:
            return []
        q = [root]
        res = []
        while q:
            size = len(q)
            t = []
            for _ in range(size):
                node = q.pop(0)
                t.append(node.val)
                if node.left is not None:
                    q.append(node.left)
                if node.right is not None:
                    q.append(node.right)
            res.append(t)
        return res[::-1]