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Perplexity·Software Engineer·Technical Phone Screen·Intermediate

Intermediate
Jun 2026

Summary

Interviewed at Perplexity for a software engineer role. The question was about outputting citation numbers from paragraphs, which sounds trivial until you're actually in the seat trying to articulate a clean approach under pressure.

Questions Asked (1)

Q1

Given a set of paragraphs where each paragraph contains numeric citations that map to a list of sources, output all the citation numbers found in the paragraphs.

Algorithms & Data StructuresTechnical Trade-offs
Author's notes

This felt deceptively simple.

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AI HintsAI Generated

Suggested Approach

Clarify the input format and citation pattern, then propose an efficient solution using regex or a parser to extract citation numbers. Discuss trade-offs between simplicity and robustness, and consider edge cases like multiple citations per paragraph and duplicate numbers.

Pro tip: Mention that you would validate the extracted numbers against the source list to handle out-of-range citations, and discuss how to scale the solution for large documents.

1. Clarify requirements

Ask about the exact format of citations (e.g., [1], (1), superscript) and whether citations can be ranges or comma-separated. Confirm if duplicates should be removed and if the output should be sorted.

2. Choose extraction method

Decide between regex-based extraction for simplicity or a more robust parser if citations are complex. Consider performance implications for large inputs.

3. Handle edge cases

Account for multiple citations in one paragraph, citations with spaces, and invalid numbers. Discuss how to handle duplicates and whether to preserve order.

4. Implement and test

Write code to extract numbers, possibly using a set to deduplicate. Test with sample paragraphs including edge cases.

5. Discuss trade-offs

Compare regex vs. parser in terms of maintainability and performance. Mention potential optimizations like streaming for large documents.

Key Points to Mention

  • Use of regular expressions to match citation patterns like \[\d+\]
  • Handling multiple citations in a single paragraph (e.g., [1,2] or [1][2])
  • Deduplication of citation numbers using a set
  • Validation of extracted numbers against the source list to avoid out-of-range citations
  • Time and space complexity analysis (O(n) time, O(k) space for k unique citations)
  • Scalability considerations for large documents (e.g., streaming or chunking)

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