Find root IDs and paths

Q: Find root IDs and paths

This question evaluates understanding of graph/tree relationships, identification of root nodes, and path reconstruction from parent references, assessing algorithmic reasoning and data-structure familiarity.

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Question

You are given a collection of string blocks, each represented as a JSON object with fields {"id": string, "parentId": string | null}. A block is a root if it has no parent (parentId is null or the referenced parent does not appear).

Write a function that returns all root ids from the input.
Follow-up: given a target id, return the path of ids from its root to that id. Explain your approach, the data structures you use, and analyze time and space complexity.

Find root IDs and paths

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