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enigma·Software Engineer·Technical Phone Screen·Intermediate

IntermediatePrefer not to say
Jul 2026

Summary

Interviewed for a software engineering role at Enigma and got a search/filtering problem that looked straightforward until you had to think about preprocessing trade-offs. Pretty algorithmic for a company I didn't expect to go deep on CS fundamentals.

Questions Asked (1)

Q1

Given a list of book titles and a query string, return all titles where at least one word matches the query by exact match (case-insensitive), prefix match, or anagram match. Then discuss trade-offs between preprocessing the data upfront versus computing matches at query time.

Algorithms & Data StructuresTechnical Trade-offsSystem Design
Author's notes

The matching logic itself wasn't too bad.

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AI HintsAI Generated

Suggested Approach

First, clarify the requirements and constraints, then outline a solution that handles exact, prefix, and anagram matches efficiently. Discuss preprocessing options like building a trie for prefixes and a hash map for anagrams, and compare with on-the-fly computation, highlighting trade-offs in time, space, and update complexity.

Pro tip: Demonstrate awareness of real-world constraints: if the book list is static, preprocessing yields faster queries; if dynamic, a hybrid approach or on-the-fly may be better. Also, mention that anagram matching can be optimized by sorting characters or using a character count signature.

1. Clarify Requirements

Ask about data size, query frequency, update frequency, and whether matches are per word or whole title. Confirm case-insensitivity and exact match definition.

2. Design Matching Logic

For each title, split into words. For each word, check exact match (lowercased equality), prefix match (startswith), and anagram match (sorted characters equality). Return titles with any matching word.

3. Optimize with Preprocessing

If queries are frequent, preprocess: build a trie for prefix matches, a hash map from sorted word to titles for anagrams, and a set for exact matches. This reduces query time to O(1) or O(prefix length).

4. Analyze Trade-offs

Compare preprocessing vs. on-the-fly: preprocessing uses more memory and requires updates when data changes, but gives faster queries. On-the-fly is simpler and uses less memory but slower per query.

5. Conclude with Recommendation

Based on assumptions (e.g., static data, high query volume), recommend a hybrid or preprocessing approach. Mention potential optimizations like caching or indexing.

Key Points to Mention

  • Time and space complexity of each matching type (exact, prefix, anagram)
  • Data structures: trie for prefix, hash map for anagrams, set for exact
  • Preprocessing costs: build time, memory overhead, update complexity
  • Query-time costs: scanning all titles vs. indexed lookup
  • Scalability considerations: number of titles, query throughput, dynamic updates
  • Hybrid approaches: e.g., preprocess anagrams and exact, but compute prefixes on the fly if prefix queries are rare

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