N-ary Tree: Sum Values, Then Link Leaves in O(1) Space

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

Problem Overview

A Citadel technical phone screen (one hour of coding, for a Data Storage / Infra-related role) asked three tree questions of rising difficulty. The first two are the graded parts here; the third is the interviewer's follow-up to Part 2. The tests build trees with a Node(val, children) class that…

  • 1 candidate-reported follow-up — 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.
Codex Fact-Checked
Technical claims, formulas, and scale numbers are reviewed against primary sources.
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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