# -- weird, I think my version is better than NC: I just don't add None nodes
class Solution:
    def rightSideView(self, root: Optional[TreeNode]) -> List[int]:
        if not root:
            return []

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

        while q:
            res.append(q[-1].val)
            for _ in range(len(q)):
                node = q.popleft()
                if node.left:
                    q.append(node.left)
                if node.right:
                    q.append(node.right)
        return res

# class Solution: NC version 
    def rightSideView(self, root: TreeNode) -> List[int]:
        res = []
        q = collections.deque([root])

        while q:
            rightSide = None
            qLen = len(q)

            for i in range(qLen):
                node = q.popleft()
                if node:
                    rightSide = node
                    q.append(node.left)
                    q.append(node.right)
            if rightSide:
                res.append(rightSide.val)
        return res