Requirements

Let's design a leader tracking system for a contest, similar to a referral leaderboard or a sales competition. The system needs to efficiently manage participants, their scores, and display the leaderboard in real-time or near real-time. Imagine you're building the backend for a popular online referral program, and participants are constantly earning points for referring new users. Maintaining an accurate and up-to-date leaderboard is crucial for user engagement and motivation. A key challenge will be handling a large number of participants and frequent score updates while ensuring the leaderboard remains accurate and responsive. We need to consider how to handle concurrent updates, efficiently rank participants, and retrieve the top performers. # Requirements ## Functional Requirements * **Register Participants:** The system must allow new participants to register for the contest. Each participant will have a unique ID and associated metadata (e.g., name, email). * **Update Scores:** The system must allow updating the score of a participant. Score updates should be atomic to prevent race conditions. We should also allow adding/subtracting scores to the current score. * **Get Leaderboard:** The system must provide a way to retrieve the leaderboard, displaying participants ranked by their scores. The leaderboard should be paginated to handle a large number of participants efficiently. We should allow retrieving top N participants. * **Get Participant Rank:** The system should provide a way to retrieve the rank of a specific participant. * **Contest Lifecycle Management:** The system must support starting and stopping the contest. When the contest is stopped, no further score updates are allowed. Support for reset/new contests. * **Tie Handling:** Define the tie-breaking strategy and implement it. This could be based on timestamp of score entry, a separate tie-breaker field, or random selection. * **Initial Score:** Allow setting the initial score when the user registers. The default score should be 0. ## Non-Functional Requirements * **Thread Safety:** The system must be thread-safe to handle concurrent score updates from multiple users. Use appropriate synchronization mechanisms (e.g., locks, atomic operations) to prevent data corruption. * **Efficiency:** The system must efficiently handle a large number of participants and frequent score updates. Consider data structures and algorithms that optimize for both score updates and leaderboard retrieval. * **Extensibility:** The system should be designed to be easily extensible to support new features, such as different scoring mechanisms or contest rules. * **Modularity:** The code should be well-modularized, with clear separation of concerns. This will make the code easier to understand, maintain, and test. * **Testability:** The system should be designed to be easily testable. Write unit tests to verify the correctness of individual components and integration tests to verify the overall system behavior. * **Maintainability:** The code should be well-documented and easy to understand, making it easier to maintain and debug. * **Scalability:** While not a distributed system design problem, consider how the core data structures might be adapted to shard the data if the single-machine capacity is exceeded (hint: think about range-based partitioning). ## Core Entities * **Participant:** Represents a participant in the contest. Attributes include a unique ID, name, email, and score. The score is a mutable property. * **Leaderboard:** Represents the overall leaderboard, responsible for ranking participants and providing access to the leaderboard data. The implementation should be efficient for rank retrieval. * **Score:** Represents the score of a participant. It should be an immutable entity. * **Contest:** Represents the contest itself. It holds the leaderboard, manages participant registration, and controls the contest lifecycle. * **Rank:** Represents the rank of a participant on the leaderboard. * **ScoreUpdateStrategy:** (Strategy pattern) Interface for different ways of updating scores.

Design a system which keeps track of leaders for some contest. Like referrals leader.

Requirements

Interview Simulation

Functional Requirements

💡 Interview Tip

Non-Functional Requirements

Core Entity Identification

Premium Content