Software Engineer · Onsite · Multiple Types

Confluent — Software Engineer

Level: Senior-Level

Round: Onsite · Type: Multiple Types · Difficulty: 8/10 · Duration: 240 min · Interviewer: Neutral

Topics: System Design, API Design, Concurrency, Database Schema, Backtracking, Binary Search

Location: San Francisco Bay Area

Interview date: 2025-08-15

Summary

Round 1: System Design (SD) - RSS

Question: Design of an RSS system, focusing on API design. The interviewer was engaged and the discussion was productive.

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Round 2: System Design (SD) - Temporary Postbox

Question: Design of a temporary postbox system, similar to TinyURL but I was not prepared for it. The interviewer seemed disengaged, and the clarification process was not smooth. We discussed concurrency and database schema, but the round ended early.

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Round 3: Coding - Combination Sum

Question: Combination Sum problem. The first part required returning true or false, and the second part required finding one solution. I used backtracking, but the interviewer didn't seem to understand it. She asked about optimizing space usage and suggested removing the for loop, but I couldn't figure out what she wanted. The experience was poor.

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Round 4: Coding - Server Downtime Check

Question: Given a set of (key, timestamp) pairs, implement a function bool wasAlive(int key, int start) to determine if the key was active in at least three consecutive 100ms intervals within the range [start, start+499]. I solved it but didn't have time to implement the binary search optimization, although I described it to the interviewer.

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Details

Preparation Tips & Key Takeaways

What I Learned

• API design is a crucial aspect of system design interviews.
• It's important to clarify requirements thoroughly at the beginning of the interview.
• Some interviewers may not be familiar with backtracking, so it's important to explain it clearly.
• Be prepared to optimize solutions for space and time complexity.

Recommended Preparation

Coding Practice

• Practice backtracking problems.
• Understand how to optimize backtracking algorithms for space and time complexity.
• Practice similar time based search problems.

System Design

• Review API design principles.
• Study system design concepts such as concurrency and database schema design.
• Be prepared to discuss trade-offs in system design.

Resources I Recommend

• LeetCode for coding problems.
• System design resources for system design concepts.

Common Pitfalls to Avoid

• Not clarifying requirements at the beginning of the interview.
• Not being able to explain backtracking clearly.
• Not being able to optimize solutions for space and time complexity.

Coding Problem

The problem description for the server downtime check was:

` Given a set of (key, timestamp) pairs, representing when a key appeared at a certain timestamp. Implement the function: bool wasAlive(int key, int start) Determine if this key has a record in at least 3 consecutive time periods within the [start, start+499] range, with each time period being 100ms.

(1, 1), (1, 101), (1, 201) -> wasAlive(1, 0) -> true (2, 1), (2, 101), (2, 301) -> wasAlive(2, 0) -> false `

LeetCode similar: LeetCode Combination Sum