Design a waitlist system with top/bottom K

## Object-Oriented Design: Waitlist System Design and implement (at the class/interface level) a **waitlist system** that supports the following operations: ### Core requirements 1. **Join the waitlist**: add a user/customer to the end of the waitlist. 2. **Leave the waitlist**: remove a specific user/customer from the waitlist. 3. **View the queue**: return the current waitlist order. 4. **Get top K**: return the first `k` users in the waitlist. 5. **Get bottom K**: return the last `k` users in the waitlist. ### Clarifications / assumptions (you may choose reasonable defaults) - Each user has a unique `userId`. - If a user tries to join twice, define the expected behavior (e.g., no-op, move to end, or error). - If `k` is larger than the queue size, return as many as possible. - Aim for clean OOD and efficient time complexity for typical operations. Provide the main classes, methods, and the data structures you would use, along with time/space complexity and key edge cases.