I got the basic structure pretty fast, sort by method priority then by date descending, then greedily walk the list.
Clarify the input/output format and edge cases, then outline a greedy algorithm that sorts payments by method priority and date descending, tracks remaining refundable amount per payment, and iterates to allocate the refund. Discuss time/space complexity and potential trade-offs with alternative approaches.
Pro tip: Mention that you would confirm whether the refund amount can be partially fulfilled and how to handle rounding or currency precision, as these details often matter in production payment systems.
Ask about input format, whether refunds can be partial, how to handle insufficient total refundable amount, and any constraints on payment methods or dates.
Propose sorting payments by method priority (CREDIT, CREDIT_CARD, PAYPAL) and within each method by date descending. Then iterate through sorted payments, allocating refunds until the total is met.
Use a map or list to track remaining refundable amount per payment after subtracting previous refunds. Accumulate refund records as you allocate.
Discuss O(n log n) time due to sorting and O(n) space. Mention that if payments are already grouped or sorted, a linear scan could suffice.
Walk through a simple example to verify correctness, including cases where refunds span multiple payments and where previous refunds reduce available amounts.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.