Design refundable transaction ledger and prioritization rules

Q: Design refundable transaction ledger and prioritization rules

This question evaluates knowledge of data structures and algorithms for transactional ledgers, including tracking payments and refundable balances, rule-based prioritization for allocating refunds, handling partial and multiple refunds, and ensuring correctness when payments and refunds interleave.

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Question

Design and implement a transaction ledger that ingests a stream of records where each record is either a payment or a refund. Each payment has {id, userId, amount, timestamp}; each refund has {id, userId, amount, timestamp, optional paymentIdReference}. (

Choose data structures to store payments and track remaining refundable amounts. (
Implement APIs: addPayment(payment), addRefund(refund, rules), and getUserBalance(userId). (
When a refund arrives without paymentIdReference, select which prior payment(s) to offset based on a provided priority rule set (e.g., a comparator that can express recency-first, amount-first, or other tie-breakers). (
Support partial refunds and multiple refunds against the same payment; ensure refunds cannot exceed a payment’s remaining refundable amount. (
Input may interleave payments and refunds; for each refund, return the list of (paymentId, refundedAmount) pairs it offsets. (
Analyze time and space complexity of each operation and justify your data-structure choices.

Design refundable transaction ledger and prioritization rules

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