Banking System (OA)

OAAnthropicLast reported July 2026High Frequency
Reported
17× across candidate reports
First seen
September 2024
Last reported
July 2026
Reported outcome
mixed

Problem Overview

Design and implement an in-memory banking system in Python on CodeSignal. The problem is split into 4 progressive levels (90 minutes total); you must pass all unit tests in one level to unlock the next. Level 1 – Core Operations: - create_account(timestamp, account_id) -> bool: Create account if it doesn't…

  • 4 candidate-reported follow-ups — 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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