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Interview question · Detection Engineering & Incident Response

Practical coding: find the top source IPs in an auth log, then do it again for an unbounded stream with fixed memory.

The first half is a Counter. The follow-up, an infinite stream and a memory cap, is the actual question: interviewers want a heavy-hitters algorithm and an honest statement of what it guarantees.

mediumNewPreparation tags: CrowdStrike, Palo Alto Networks, GoogleUpdated Nov 2026

The first half is a Counter. The follow-up, an infinite stream and a memory cap, is the actual question: interviewers want a heavy-hitters algorithm and an honest statement of what it guarantees.

Make your first attempt

What would you say before reading the answer?

  1. 01 State the assumptions your answer depends on.
  2. 02 Explain the mechanism and choose a control.
  3. 03 Name a condition that would change your decision.

The worked answer includes an approach, scoring criteria and follow-up questions. Compare the reasoning with your own.

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What if · the follow-ups in this answer

The answer works through 6 follow-ups like an interviewer would

You must find the top IP addresses by traffic in a high-volume network stream on a sensor with fixed memory, to spot possible exfiltration or abuse.

  1. How would you do it if the data fit in memory?
  2. Why does that fail on an unbounded stream?
  3. How does Misra-Gries work?
  4. When would you use a Count-Min Sketch instead?
  5. How do you report results responsibly?
  6. What approach would you choose?

Each rung has a nudge, a model answer, the principle that carries over and the weak answer to avoid. Premium opens every answer and ladder.

UP NEXT ON YOUR JOURNEY
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