Social Network: Followers, Snapshots and Recommendations

CodingOpenAILast reported September 2026High Frequency
Reported
21× across candidate reports
First seen
December 2025
Last reported
September 2026
Reported outcome
mixed

Problem Overview

OpenAI coding question, reconstructed from 21 candidate reports (December 2025 to September 2026). Tests: time-based state (expiry, TTL, snapshots); hash-map counting, grouping and joins. Candidates reported 6 follow-ups. The write-up includes a Python solution that passes 8 test cases.

  • 6 candidate-reported follow-ups — the probes candidates report being asked, with the trigger for each
  • The full 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. Follow-ups candidates reported, not invented ones.
Codex Fact-Checked
Technical claims, formulas, and scale numbers are reviewed against primary sources.
Interviewer Follow-ups
The follow-ups candidates reported, with the trigger that prompts each one — plus the mistakes that sink people.
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