Order Book / Matching Engine Implementation

CodingCitadelLast reported July 2026Medium Frequency
Reported
4× across candidate reports
First seen
September 2025
Last reported
July 2026
Reported outcome
mixed

Problem Overview

Build an order book in a live coding round. Four reports describe it: two as 45-minute rounds (one of them on CoderPad), one as pair coding in the first of four one-hour rounds. The reports leave the design to you. In one round the interviewer's first question was which APIs…

  • 1 candidate-reported follow-up — the exact probes interviewers asked, with the trigger for each
  • The rest of the problem statement — full requirements, constraints, and edge cases
  • Approach and trade-offs — what passing candidates did, and the mistakes that sink people
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Verified Source
Every question is reconstructed from multiple independent candidate reports. Verbatim follow-ups, not invented ones.
Codex Fact-Checked
Technical claims, formulas, and scale numbers are reviewed against primary sources.
Interviewer Follow-ups
The exact follow-ups reported by candidates, with the trigger that prompts each one — plus the mistakes that sink people.
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