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Design a Group Expense-Splitting Ledger Object-Oriented Design Interview

Design a system where users form groups, log shared expenses using pluggable splitting strategies (equal/exact/percentage), maintain pairwise balances, and settle debts.

Mock Interview with AI

1. Problem Statement

Design a group expense-splitting ledger: users form groups, any member can log a shared expense split equally, by exact amount, or by percentage, the system tracks running pairwise balances, and users can settle debts fully or partially.

2. Live Coding Format

Work in the provided coding workspace while explaining your decisions to the live interviewer. Validation may use inline tests, examples, comments, or a verbal walkthrough.

3. Key Focus Areas

1
Split strategy abstraction (equal/exact/percentage)
2
Expense and Group entity modeling
3
Pairwise balance consistency
4
Settlement handling (full/partial)
5
Debt-simplification as a stretch extension

4. What Strong Candidates Should Demonstrate

✓Use the Strategy pattern so new split types do not require editing Expense or Ledger.
✓Keep pairwise balance bookkeeping consistent as expenses and settlements accumulate.
✓Validate percentage/exact splits sum correctly before committing an expense.
✓Reason about extending the design toward debt-simplification (minimizing settlement transactions).

Want interactive feedback?

Practice this problem in the live coding workspace while the interviewer probes your clarification, implementation, trade-offs, and validation.

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Core Concepts

Object-Oriented DesignStrategy PatternLedger Modeling