Design a delivery cost system

Q: Design a delivery cost system

This question evaluates the ability to design an object-oriented in-memory delivery cost and payment accounting system, focusing on modeling time intervals, prorated duration calculations, currency rounding, idempotent payment semantics, time zone handling, numeric precision, and time/space complexity.

Q: How do I approach System Design interview questions?

System Design questions require understanding of core concepts and practice. PracHub provides solutions with explanations to help you master system design interviews.

Q: What difficulty level is this interview question?

This is a medium difficulty System Design question, commonly asked during Technical Screen rounds at Rippling.

Q: What role is this question designed for?

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

Question

Object-Oriented Delivery Cost and Payment Accounting System

Context

You are designing a small in-memory service to track delivery costs for drivers who are paid hourly. Deliveries are recorded with start and end timestamps. The system must compute total cost to date, support marking accrued costs up to a timestamp as paid, and report remaining unpaid amounts.

Make explicit assumptions about time interval semantics (inclusive/exclusive), how to prorate partial hours, and how to round currency.

Requirements

Drivers register with an hourly rate (and may be updated):
- RegisterDriver(driverId, hourlyRate)
Record deliveries:
- RecordDelivery(driverId, startTime, endTime)
Aggregate queries:
- getTotalCost() → sum over all deliveries of hourlyRate(driverId) × duration
- payUpTo(timestamp) → mark all accrued costs up to timestamp as paid. If a delivery overlaps the timestamp, only the portion up to timestamp is paid (logically split at the timestamp).
- getTotalUnpaid() → total remaining unpaid amount after all payUpTo calls.

Deliverables

Class design and core data structures
Method signatures
Define: interval inclusivity/exclusivity; partial hours handling and rounding strategy
Discuss: idempotency, time zones, numeric precision, and time/space complexity

Design a delivery cost system

Quick Overview

Object-Oriented Delivery Cost and Payment Accounting System

Context

Requirements

Deliverables

Solution

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