class Solution:
    def zigzagLevelOrder(self, root: Optional[TreeNode]) -> List[List[int]]:
        if not root:
            return []

        q = deque([root])
        level = 1
        res = []

        while q:
            if (level % 2): ## < this is nice
                res.append([x.val for x in q])
            else:
                res.append([x.val for x in reversed(q)])
            for _ in range(len(q)):
                node = q.popleft()
                if node.left:
                    q.append(node.left)
                if node.right:
                    q.append(node.right)
            level += 1
        return res