Leetcode 107. Binary Tree Level Order Traversal II

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def levelOrderBottom(self, root: TreeNode) -> List[List[int]]:
        if not root: return []
        q = [root, None]
        ans = []
        temp = []
        
        while q:
            node = q.pop(0)
            if node is None:
                if q: q.append(None)
                ans.append(temp)
                temp = []

                continue
            else:
                if node.left:
                    q.append(node.left)
                if node.right:
                    q.append(node.right)
                temp.append(node.val)
                
        return reversed(ans)

https://leetcode.com/problems/binary-tree-level-order-traversal-ii/