Design delivery driver payment system
Overview
This question evaluates system design and engineering skills related to in-memory payroll services, covering time-interval merging and overlap handling, accurate monetary accounting, API and state-mutation design, and reasoning about correctness under unordered event insertion.
Rippling
Jul 29, 2025, 8:05 AM
Software Engineer
Technical Screen
System Design
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Design a Delivery Driver Salary System
You are designing an in-memory payroll service that calculates and pays delivery drivers based on their worked time. The system must provide accurate cost accruals, support partial payments up to a boundary time, and avoid double-paying overlapping work intervals.
Assumptions (make minimal changes if needed):
- Time values are Unix timestamps in seconds; intervals use half-open semantics [start_time, end_time).
- Each driver has a constant USD hourly rate after Add_driver (rate changes are out of scope but can be added as an extension).
- Record_delivery only records completed deliveries (end_time > start_time). Deliveries can be inserted out of chronological order.
- For a given driver, overlapping or adjacent delivery intervals should be merged so the driver is not double-paid for the same minute twice.
- Monetary values are tracked in integer cents to avoid floating-point error.
APIs to support:
- Add_driver(driver_id, usd_hourly_rate)
- Record_delivery(driver_id, start_time, end_time)
- Get_Total_Cost()
- Pay_Up_To(pay_time)
- Total_Cost_Unpaid()
Explain:
- Data structures to store drivers, delivery intervals, rates, and payments.
- State-mutation logic for each API, including handling overlaps and partial payments.
- Object-oriented design that enables accurate and efficient payroll computation, plus complexity trade-offs.
Solution
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