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Stripe·Software Engineer·Technical Phone Screen·Intermediate

Intermediate
Apr 2026

Summary

Stripe software engineering interview with a CSV parsing and validation problem. The question was more about careful rule implementation than raw algorithmic cleverness, which I didn't fully appreciate until I was halfway through writing broken logic.

Questions Asked (1)

Q1

Given a CSV string with a header row and data rows, output VERIFIED or NOT_VERIFIED for each data row based on four rules: all 6 fields must be non-empty, the fifth column must be between 5 and 31 characters, the second column must not contain any blocklisted words, and the second column must share at least 50% of its words (case-insensitive) with either the fourth or fifth column.

Algorithms & Data StructuresTechnical Trade-offsAPI & Integrations
Author's notes

The word-overlap rule is where I fumbled.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the problem: confirm CSV parsing rules (e.g., quoted fields, commas inside quotes), blocklist source, and word definition. Then outline a modular solution: parse rows, apply each rule with early exit, and output results. Emphasize edge cases and testability.

Pro tip: Mention that you'd use a proper CSV parser rather than naive split to handle quoted fields and escaped commas, and discuss how to efficiently check word overlap using sets.

1. Clarify requirements and edge cases

Ask about CSV format specifics (quoting, escaping), blocklist source, and word tokenization rules. Confirm output format and whether header is always present.

2. Design parsing and validation pipeline

Outline a function that parses CSV into rows, then for each data row applies the four rules in order, short-circuiting on failure. Use a CSV library or implement a robust parser.

3. Implement each rule with helper functions

Create helpers: check_non_empty(fields), check_length(field5, 5, 31), check_blocklist(field2, blocklist), check_word_overlap(field2, field4, field5, 0.5). Use case-insensitive comparison and set operations for overlap.

4. Handle edge cases and test

Consider empty input, missing columns, quoted fields with commas, and words with punctuation. Write unit tests for each rule and integration tests for the full pipeline.

5. Discuss trade-offs and optimizations

Talk about time/space complexity, early exit, and potential optimizations like precompiling blocklist regex or caching word sets. Mention scalability for large CSVs.

Key Points to Mention

  • Use a proper CSV parser to handle quoted fields and escaped commas, not naive split.
  • Apply rules in order with early exit to avoid unnecessary computation.
  • For word overlap, tokenize case-insensitively, use sets, and compute intersection size / max(len(set2), len(set4/5)) >= 0.5.
  • Blocklist check should be case-insensitive and consider word boundaries to avoid false positives.
  • Length check: fifth column must be between 5 and 31 characters inclusive.
  • Discuss testing strategy: unit tests for each rule, edge cases like empty fields, missing columns, and quoted commas.

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