## Problem Design a `CreditScoreSystem` that manages user credit scores. Starting score is 700 for every new user. Implement the following operations: - `add_user(user_id)` -- register a new user. - `record_payment(user_id, on_time: bool)` -- on-time payment adds 10 points; missed payment subtracts 40 points. Score is clamped to [300, 850]. - `get_score(user_id) -> int` -- return current score. - `top_k(k: int) -> list[str]` -- return the k users with the highest scores (ties broken by `user_id` lexicographically). ```python class CreditScoreSystem: def add_user(self, user_id: str) -> None: ... def record_payment(self, user_id: str, on_time: bool) -> None: ... def get_score(self, user_id: str) -> int: ... def top_k(self, k: int) -> list[str]: ... ``` **Example:** ``` sys.add_user("alice"); sys.add_user("bob") sys.record_payment("alice", True) # alice -> 710 sys.record_payment("bob", False) # bob -> 660 sys.top_k(1) -> ["alice"] ``` ## Follow-ups 1. How would you make `top_k` efficient if there are 50 million users? 2. Add a `history(user_id) -> list[int]` method returning all score snapshots. What is the storage impact? 3. How do you handle concurrent `record_payment` calls for the same user in a multithreaded context?

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Credit Score System: Design a Class That Tracks User Transactions and Updates Credit Score

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Problem Design a CreditScoreSystem that manages user credit scores. Starting score is 700 for every new user. Implement the following operations: add_user(user_id) -- register a new user. record_payment(user_id, on_time: bool) -- on-time payment adds 10 points; missed payment subtracts 40 points. Score is clamped to [300, 850]. get_score(user_id) -> int -- return current score. top_k(k: int) -> list[str] -- return the k users with the highest scores (ties broken by user_id lexicographically). Ex…

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Credit Score System: Design a Class That Tracks User Transactions and Updates Credit Score

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