Todo List / Collaborative To-Do System Design

Problem Overview

Design a collaborative to-do list application. Users should be able to create to-do lists and individual tasks, share lists with other users, and concurrently edit the same list in real time. The system must handle multi-user synchronization, real-time update notifications, and read/write conflict resolution…

• 5 candidate-reported follow-ups — the exact probes interviewers asked, with the trigger for each
• The rest of the problem statement — full requirements, constraints, and edge cases
• Approach and trade-offs — what passing candidates did, and the mistakes that sink people