Given a binary tree in level-order list form, convert it into its mirror by swapping every node's left and right children. Your task is to return the mirrored tree in the same compact level-order format, using `None` for missing children when needed and removing trailing `None` values. In an interview, you should also be able to explain both approaches: 1. A recursive DFS solution 2. An iterative solution using a stack or queue Edge cases to think about include an empty tree, a single-node tree, and a highly unbalanced tree. Dry run for `[5, 3, 8, None, 4, 7, 9]`: - Swap children of `5` -> left becomes `8`, right becomes `3` - Swap children of `8` -> left becomes `9`, right becomes `7` - Swap children of `3` -> left becomes `4`, right becomes `None` Final mirrored tree in level order: `[5, 8, 3, 9, 7, 4]`