Tree Traversal: Find Invalid / Root Nodes

CodingZipLast reported November 2025Medium Frequency
Reported
6× across candidate reports
First seen
February 2025
Last reported
November 2025
Reported outcome
mixed

Problem Overview

You are given a collection of nodes, each represented as a JSON object (or similar structure) containing: a node ID, a parent ID (null/absent for root nodes), and a level/depth field indicating which level of the tree the node sits on. Your tasks: (1) Identify all root nodes (nodes whose…

  • 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.
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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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