Distributed Machine Count (Tree Network)

Also reported as Machine Topology · Machine Tree: Count and Topology · Cluster Message Aggregation

CodingOpenAILast reported September 2026High Frequency

Reported: 20× across candidate reports
First seen: January 2025
Last reported: September 2026
Also asked in: Phone Screen
Reported outcome: mixed

Problem Overview

OpenAI coding question, reconstructed from 20 candidate reports (January 2025 to September 2026). Tests: tree recursion and traversal; concurrency and thread safety. Candidates reported 2 follow-ups. The write-up includes a Python solution that passes 6 test cases.

2 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.