Flatten & Unflatten Nested Structure

Phone ScreenxAILast reported February 2026Low Frequency
Reported
1× across candidate reports
First seen
February 2026
Last reported
February 2026
Reported outcome
unknown

Problem Overview

xAI phone-screen question, reconstructed from 1 candidate report (February 2026). Tests: tree recursion and traversal. The write-up includes a Python solution that passes 8 test cases.

  • 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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