0199：二叉树的右视图（★）

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class Solution:
    def rightSideView(self, root: Optional[TreeNode]) -> List[int]:
        res,Q = [],[root] if root else []
        while Q:
            res.append(Q[-1].val)
            Q = [c for u in Q for c in [u.left,u.right] if c]
        return res