← Hudson River Trading Interview Insights

Hudson River Trading·Software Engineer·Technical Phone Screen·Senior

SeniorPrefer not to say
May 2026

Summary

HRT quant researcher technical screen, basically one meaty C++ design problem that ate up the whole session. The question was more systems-flavored than I expected for a quant role, which threw me a bit.

Questions Asked (1)

Q1

Design and implement a C++ template class that wraps either std::map or std::unordered_map, with key and value types each independently parameterizable as int or string. The class should support insert/update, lookup, remove, size, and iteration, and handle the empty container case correctly. Be prepared to discuss template specialization strategies and how you keep behavior consistent across both underlying container types.

System DesignTechnical Trade-offsAlgorithms & Data Structures
Author's notes

I started with the template parameters and immediately second-guessed whether to use full specialization or just let the compiler handle it through partial specialization.

Create a free account to read the full note

AI HintsAI Generated

Suggested Approach

Start by clarifying requirements and constraints, then propose a template class that abstracts the underlying map via a policy or template template parameter, ensuring a consistent interface. Discuss how to handle key/value type combinations using template specialization or SFINAE, and outline the implementation of core operations with attention to edge cases like empty containers.

Pro tip: Emphasize that you would use a template template parameter to parameterize the container type, which avoids code duplication and makes the wrapper extensible to other map-like containers. Also, mention that you would provide a uniform iteration interface by exposing begin/end and ensuring const-correctness.

1. Clarify Requirements and Constraints

Ask about expected usage patterns, performance requirements, and whether the underlying container should be selectable at compile-time or runtime. Confirm that key and value types are limited to int and string, and that the interface must be consistent.

2. Design the Template Interface

Propose a class template with parameters for key type, value type, and the underlying container (using a template template parameter). Define the public API: insert/update, lookup, remove, size, and iteration methods.

3. Handle Type Combinations and Specialization

Discuss how to support all four key-value combinations (int-int, int-string, string-int, string-string) without code bloat. Consider using partial specialization or a traits class to map types to appropriate comparators/hash functions.

4. Implement Core Operations and Edge Cases

Outline the implementation of each method, ensuring they delegate to the underlying container. Address empty container behavior for lookup (return optional or throw), remove (no-op or return bool), and iteration (empty range).

5. Ensure Consistency and Discuss Trade-offs

Explain how you maintain identical semantics across std::map and std::unordered_map, such as ordering guarantees (or lack thereof) and complexity. Discuss trade-offs like performance vs. interface simplicity.

Key Points to Mention

  • Template template parameter to parameterize the underlying container (e.g., template<template<class...> class Map>).
  • Use of std::conditional or type traits to select appropriate comparator/hash for int and string keys.
  • Handling of empty container: lookup returns std::optional or throws, remove returns bool, iteration yields empty range.
  • Consistent interface: methods like insert_or_assign, find, erase, size, begin/end.
  • Trade-offs: std::map provides ordered iteration and O(log n) operations; std::unordered_map provides average O(1) but no order.
  • Avoiding code duplication via generic programming and policy-based design.

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