Confluent·Software Engineer·Technical Phone Screen·Intermediate

IntermediatePrefer not to say

Jun 2026

Summary

Coding round at Confluent for a software engineer role. The question was a classic tail -n implementation, but the setup requirement ate up most of the time and I never got to the follow-up.

Questions Asked (1)

Implement a version of the Unix `tail -n` command that reads the last N lines from a file.

Algorithms & Data StructuresTechnical Trade-offs

Author's notes

The part that killed me wasn't the algorithm, it was that the interviewer wanted me to write a txt file first and read from it as test input.

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AI HintsAI Generated

Suggested Approach

Start by clarifying requirements (file size, N, memory constraints, whether the file can be loaded entirely). Then present a solution that reads the file from the end using a circular buffer of size N, which is optimal for large files. Discuss trade-offs between this approach and simpler ones like reading all lines into memory, and mention edge cases.

Pro tip: Mention that you would use a circular buffer to store the last N lines while reading the file backwards, which avoids storing the entire file in memory. Also, proactively discuss how to handle files that are too large to fit in memory and the importance of seeking to the end efficiently.

1. Clarify Requirements

Ask about file size, N, memory constraints, and whether the file can be read multiple times. Confirm if the solution should handle stdin or only files.

2. Choose an Approach

Decide between reading the entire file into memory (simple but memory-heavy) and reading from the end using a circular buffer (efficient for large files). Explain the trade-offs.

3. Design the Algorithm

For the efficient approach: seek to the end, read backwards in chunks, split into lines, and maintain the last N lines using a circular buffer. Handle line boundaries correctly.

4. Handle Edge Cases

Consider N=0, N larger than total lines, empty file, file without trailing newline, and very long lines. Discuss how to handle these gracefully.

5. Analyze Complexity and Optimize

State time complexity O(file size) and space complexity O(N). Mention possible optimizations like using memory-mapped files or parallel processing if needed.

Key Points to Mention

Circular buffer for storing last N lines efficiently
Reading file backwards to avoid loading entire file into memory
Time and space complexity analysis (O(file size) time, O(N) space)
Edge cases: N=0, N > total lines, empty file, no trailing newline
Trade-offs between simple in-memory approach and streaming approach
Handling of very large files and memory constraints

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