Rectangle Board: Add, Count, Remove and Undo

CodingOpenAILast reported October 2026Low Frequency

Problem Overview

OpenAI coding question, reconstructed from 2 candidate reports (October 2026). The write-up includes a Python solution that passes 16 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.