## Problem Design the core data structure and merge logic for a collaborative plain-text editor. Two users can edit the same document concurrently; your system must merge their changes without data loss. ```python class Document: def __init__(self, text: str): ... def apply(self, op: 'Operation') -> 'Document': ... def transform(self, op: 'Operation', against: 'Operation') -> 'Operation': ... class Operation: # Sequence of: retain(n), insert(s), delete(n) def __init__(self, ops: list): ... ``` **Example:** ``` Base: "hello" Alice: insert " world" at index 5 -> "hello world" Bob: delete "h" at index 0 -> "ello" Merged result: "ello world" ``` ## Follow-ups 1. What invariant must hold between `base_length` and `target_length` for two operations to be composable? 2. How does your transform handle the case where both users delete the same character? 3. Why might CRDTs be preferred over OT for a distributed system with no central server? 4. How would you checkpoint document history to allow undo across sessions?

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Text Document: Build a Collaborative Plain-Text Document Editor with Operational Transforms

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Problem Design the core data structure and merge logic for a collaborative plain-text editor. Two users can edit the same document concurrently; your system must merge their changes without data loss. Example: Follow-ups What invariant must hold between base_length and target_length for two operations to be composable? How does your transform handle the case where both users delete the same character? Why might CRDTs be preferred over OT for a distributed system with no central server? How would…

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This is a candidate experience report from a notion interview during the phone round.

It covers the following topics: System Design, Coding, Phone, Onsite .

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Text Document: Build a Collaborative Plain-Text Document Editor with Operational Transforms

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