Level Order

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

Return level-order traversal as a list of levels. Treat this as a production helper: match the contracted return shape, including empty and duplicate inputs.

A tree report needs rows grouped by depth so each level can be displayed or processed separately. Return a list of lists. The first inner list contains the root, the next contains its children, and so on from left to right. Write level_order(level_order_input: list) -> list. The sample tree produces [[3], [9, 20], [15, 7]]. The starter file already has the function name and harness print lines. Keep them and fill only the function body.

Requirements

• Visit nodes breadth first.
• Keep left-to-right order inside each level.
• Return one inner list per visited level.

Constraints

• The input is level-order with None placeholders.
• The return type is a list of lists.

Examples

Input: level_order([3, 9, 20, None, None, 15, 7]) Output: [[3], [9, 20], [15, 7]] 3 levels.

Topics: lakebench, python, bfs, levels.

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