Design payment scheduler with cancel and top-K outgoing

Q: Design payment scheduler with cancel and top-K outgoing

This question evaluates knowledge of designing stateful in-memory services, efficient data structures and algorithms for scheduled task execution and top‑K outgoing aggregation, and correctness in handling cancellation, failure semantics, and related edge cases.

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Coding & Algorithms questions require understanding of core concepts and practice. PracHub provides solutions with explanations to help you master coding & algorithms interviews.

Q: What difficulty level is this interview question?

This is a Medium difficulty Coding & Algorithms question, commonly asked during Take-home Project rounds at Circle.

Q: What role is this question designed for?

This question is commonly asked for Software Engineer candidates at Circle during technical interviews.

Question

Design and implement an in-memory banking payment component with the following APIs: (

schedulePayment(payerId, payeeId, amount, executeAt) -> paymentId: create a pending outgoing payment scheduled for executeAt. (
cancelPayment(paymentId) -> boolean: cancel only if still pending. (
removePayment(paymentId) -> boolean: allow deletion only if the payment is CANCELED or FAILED; successful payments cannot be removed. (
processDuePayments(now): execute all pending payments with executeAt <= now; mark each as SUCCESS if funds are sufficient, otherwise FAILED; only successful payments contribute to outgoing totals. (
getTopKByOutgoingTotal(k) -> list <accountId> : return accountIds sorted by descending total outgoing amount from successful payments only; break ties by smaller accountId. Requirements: support only outgoing flow tracking (no incoming totals). Define the data structures to support efficient scheduling, cancellation, removal, and top-k queries; provide the time and space complexity of each API. Describe how you handle edge cases such as canceling an already executed payment, repeated cancellations, removing non-existent or ineligible payments, and ensuring that canceled payments are not executed.

Design payment scheduler with cancel and top-K outgoing

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