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Aggregate expenses by person, trip, and category

RipplingSoftware Engineer · Onsite
MediumSoftware EngineerOnsiteCoding & Algorithms

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This question evaluates a candidate's ability to perform efficient data aggregation, use associative data structures (maps/dictionaries), and reason about time and space complexity when processing large collections of records.

Problem

You are given a list of expense records. Each record has:

  • employee_id (string)
  • trip_id (string)
  • category (string, e.g., MEAL, HOTEL, TRANSPORT)
  • amount (integer)

Implement functions to compute aggregated totals:

  1. Per-employee total
  • Return total spend for each employee_id.
  1. Per-trip breakdown (for one employee)
  • Given an employee_id, return total spend per trip_id.
  1. Per-category breakdown (for one employee)
  • Given an employee_id, return total spend per category.

Input/Output expectations

  • Input: an array/list of expense records.
  • Output: maps/dictionaries for each query type.

Constraints

  • Up to 10^6 expense records.
  • Aim for efficient time complexity; avoid re-scanning the full list for every query.