Confluent·Software Engineer·Technical Phone Screen·Senior

Senior

May 2026

Summary

Confluent SWE interview that was basically a systems-flavored coding question disguised as a design discussion. They gave you a stripped-down file API and asked you to rebuild Unix tail, then pushed on the trade-offs between two different approaches. More open-ended than I expected for a technical screen.

Questions Asked (1)

Implement the equivalent of Unix `tail -n` using a minimal file API (read, move_pointer, get_size). Write pseudocode and discuss the trade-offs between a forward linear scan with a rolling buffer versus a backward seek approach.

System DesignTechnical Trade-offsAlgorithms & Data Structures

Author's notes

The two-approach discussion is where I spent most of my energy.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the API constraints and edge cases (e.g., n larger than file size, empty file). Then present pseudocode for both approaches, highlighting the time/space trade-offs and when each is preferable. Finally, discuss optimizations like block-based backward reads and the importance of handling partial lines.

Pro tip: Mention that in real systems, the backward seek approach is often preferred for large files because it avoids reading the entire file, but it requires careful handling of buffer boundaries and partial lines. Also, note that the forward scan is simpler and more robust for small files or when the file is already in cache.

1. Clarify requirements and constraints

Ask about the file API details (e.g., can we seek to arbitrary positions? Is the file size known upfront?) and edge cases (n=0, n > file size, empty file, very large lines).

2. Design forward linear scan with rolling buffer

Pseudocode: read file sequentially, maintain a circular buffer of the last n lines. At EOF, output the buffer. Discuss time O(file size), space O(n * max line length).

3. Design backward seek approach

Pseudocode: start from end, read blocks backwards, count newlines until n+1 found, then output from that point. Handle partial lines at block boundaries. Discuss time O(bytes read from end), space O(block size).

4. Compare trade-offs

Forward scan: simple, works with any API, but reads entire file. Backward seek: efficient for large files, but complex and requires seeking. Consider file size, n, line length, and API capabilities.

5. Discuss optimizations and real-world considerations

Mention block-based reading to reduce I/O, using a dynamic buffer for lines, and handling files without trailing newline. Relate to Confluent's need for efficient log tailing.

Key Points to Mention

Time and space complexity of each approach
Edge cases: n=0, n > number of lines, empty file, file without trailing newline
Buffer management: circular buffer vs. dynamic array, handling partial lines
API constraints: whether move_pointer supports seeking from end, get_size availability
Performance implications: I/O cost, memory usage, suitability for large files
Real-world analogy: Unix tail implementation, log tailing in distributed systems

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.