Tree Pre-Order Traversal with Marked Invalid Nodes

Phone ScreenSnowflakeLast reported December 2025Low Frequency

Reported: 1× across candidate reports
First seen: December 2025
Last reported: December 2025
Reported outcome: unknown

Problem Overview

Snowflake phone-screen question, reconstructed from 1 candidate report (December 2025). Tests: tree recursion and traversal. The write-up includes a Python solution that passes 6 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.

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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.