Implement a Credit Tracker Class
Last updated: September 4, 2025
Quick Overview
Implement a CreditTracker with add_credit, subtract_credit, and check_credit methods. Handle thread-safety for concurrent access.
Perplexity
Coding & Algorithms
Software Engineer
Perplexity
September 4, 2025Software Engineer
Technical Phone Screen
Coding & Algorithms
Easy
14
4
2,709 solved
Implement a CreditTracker with add_credit, subtract_credit, and check_credit methods. Handle thread-safety for concurrent access.
Simple OOP problem reported at Perplexity. Tests basic class design with concurrency follow-ups for managing user API quotas.
What the Interviewer Expects
- Implement clean class interface with proper encapsulation
- Handle negative balance prevention
- Add thread-safety with locks
- Support multiple users with isolated balances
- Write comprehensive edge case tests
Key Topics to Cover
OOP design
Thread safety
Concurrency
API rate limiting
Class encapsulation
How to Approach This
- Clarify input constraints and edge cases before writing code.
- Walk through your approach verbally and confirm with the interviewer before coding.
- Start with a brute force solution, then optimize. Mention time and space complexity.
- Test your solution with examples, including edge cases like empty input or duplicates.
- Consider common patterns: sliding window, two pointers, hash map, BFS/DFS, dynamic programming.
Possible Follow-up Questions
- How would you persist credit balances across restarts?
- What if credits expire after a time period?
- How would you handle distributed credit tracking across multiple servers?
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Problem Analysis
The problem requires implementing a CreditTracker class with methods to add, subtract, and check credits while ensuring thread safety. The primary pattern here is the use of thread locks to manage...
Approach
- Class Definition: We will define a
CreditTrackerclass that holds a dictionary to maintain user balances. - Method Implementations:
- add_credit(user_id, amount): Increments the u...
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