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Heygen·Software Engineer·Technical Phone Screen·Intermediate

Intermediate
May 2026

Summary

Coding round at Heygen for a software engineer role. One problem, but the real challenge was figuring out what the problem actually was since the interviewer wouldn't clarify anything upfront.

Questions Asked (1)

Q1

Given a paragraph string and a list of (substring, annotation) pairs, write a function that wraps every occurrence of each substring in an XML tag using its corresponding annotation. You're expected to surface and resolve edge cases yourself since the interviewer won't bring them up.

Algorithms & Data StructuresTechnical Trade-offsAdaptability & Ambiguity
Author's notes

The function itself isn't that bad once you sit down and think about it.

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AI HintsAI Generated

Suggested Approach

Start by clarifying requirements and enumerating edge cases (overlapping matches, nested annotations, special characters, multiple annotations for the same substring, and empty inputs). Then propose a robust algorithm that handles these cases, such as interval-based conflict resolution, and discuss trade-offs between simplicity and correctness. Finally, outline a test plan covering normal and edge cases.

Pro tip: Proactively discuss how to handle overlapping matches by defining a clear precedence rule (e.g., longest match wins, or earliest start then longest) and mention that XML escaping of the original text is necessary to avoid invalid output.

1. Clarify Requirements and Edge Cases

Ask questions to understand expected behavior for ambiguous scenarios: overlapping substrings, nested annotations, multiple annotations for the same substring, case sensitivity, and special characters. Confirm the output format and whether XML escaping is required.

2. Design the Algorithm

Choose an approach that finds all matches, resolves conflicts (e.g., by sorting intervals and selecting non-overlapping ones based on a precedence rule), and then constructs the output string with tags inserted at the correct positions.

3. Implement and Handle Edge Cases

Write clean code that handles empty inputs, no matches, and special characters. Ensure that the original text is XML-escaped and that tags are properly nested or non-overlapping as per the chosen rule.

4. Test and Validate

Walk through test cases including simple matches, overlapping matches, nested annotations, multiple annotations for the same substring, and strings with XML special characters. Verify the output is well-formed XML.

5. Discuss Trade-offs and Extensions

Explain the trade-offs of your approach (e.g., time complexity, simplicity vs. handling complex overlaps) and suggest possible extensions like supporting regex or handling nested tags if needed.

Key Points to Mention

  • Overlapping matches: define a precedence rule (e.g., longest match, earliest start) and resolve conflicts by selecting non-overlapping intervals.
  • Nested annotations: decide whether to allow nesting (e.g., <a><b>text</b></a>) or flatten; if nesting, ensure proper tag ordering.
  • Multiple annotations for the same substring: specify behavior (e.g., apply all in order, or only the first) and handle accordingly.
  • XML escaping: escape special characters (&, <, >, ", ') in the original text to produce valid XML.
  • Case sensitivity: clarify whether matching is case-sensitive and handle accordingly.
  • Performance: discuss time complexity (e.g., O(n*m) for naive search) and potential optimizations like using Aho-Corasick for multiple substrings.

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