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Invert Binary Tree

Python data engineering interview problem. Difficulty: advanced. Pattern: Trees. About 18 minutes. Part of the Pro drill bank.

Invert a binary tree given as a level-order list. Treat this as a production helper: match the contracted return shape, including empty and duplicate inputs.

Implement invert_tree(level_order: list) -> list. Input/output use level-order lists with None for missing children (trailing Nones may be omitted).

Constraints

  • Include helpers inside the solution.

Examples

Input: invert_tree([4, 2, 7, 1, 3, 6, 9]) Output: [4, 7, 2, 9, 6, 3, 1] Children swapped at every node.

Topics: lakebench, python, invert, level-order.

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Invert Binary Tree

Interview-style drill: Invert a binary tree given as a level-order list.

Implement `invert_tree(level_order: list) -> list`. Input/output use level-order lists with `None` for missing children (trailing Nones may be omitted). Example: `[4, 2, 7, 1, 3, 6, 9]` → `[4, 7, 2, 9, 6, 3, 1]`. Keep the harness.