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Stripe·Software Engineer·Technical Phone Screen·Intermediate

Intermediate
May 2026

Summary

Stripe SWE screening with a KYC validation coding problem. Pretty focused on string handling and filtering logic, nothing too wild but the dual-rule constraint tripped me up a bit.

Questions Asked (1)

Q1

Given a list of records (each record is a list of field values), validate each record against two rules: column 5 must be at most 50 characters long, and column 2 must not contain any substring from a provided forbidden words list (case-sensitive). Return only the records that pass both rules.

Algorithms & Data StructuresAPI & Integrations
Author's notes

I jumped straight to iterating over records and forgot for a second that the columns are 1-indexed, so my first pass was off by one.

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AI HintsAI Generated

Suggested Approach

First clarify the input format and edge cases, then propose a single-pass solution that checks both rules per record, short-circuiting on failure. Write clean code with helper functions for each rule, and analyze time and space complexity.

Pro tip: Mention that you'd preprocess the forbidden words into a set or trie for efficient substring matching, and discuss trade-offs between simplicity and performance. Also, proactively ask about case sensitivity and empty lists to show attention to detail.

1. Clarify requirements and edge cases

Ask about input format, data types, empty records, missing columns, and whether forbidden words can be empty. Confirm case sensitivity and length definition (e.g., Unicode characters vs bytes).

2. Outline the algorithm

Propose iterating through each record, checking rule 1 (column 5 length ≤ 50) and rule 2 (no forbidden substring in column 2). Use short-circuit evaluation to skip unnecessary checks.

3. Implement with helper functions

Write a function that takes a record and returns a boolean. Use separate helpers for length check and forbidden substring check, making the code modular and testable.

4. Optimize substring search

Discuss using a set for exact matches or a trie/Aho-Corasick for multiple substring patterns. For small lists, a simple loop is fine; mention trade-offs.

5. Analyze complexity and test

State time complexity O(n * (m + k * L)) where n is records, m is column 5 length, k is forbidden words, L is average word length. Space O(1) extra. Walk through test cases.

Key Points to Mention

  • Input validation and handling missing or malformed records
  • Case-sensitive substring matching and efficient data structures (set, trie)
  • Short-circuit evaluation to avoid unnecessary checks
  • Time and space complexity analysis
  • Modular code with helper functions for readability and testing
  • Edge cases: empty list, empty forbidden words, records with fewer than 5 columns

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