rippling·Software Engineer·Technical Phone Screen·Senior

SeniorPrefer not to say

May 2026

Summary

Rippling coding interview, one question but it had enough moving parts to keep me busy for the whole session. The problem was about extending a poker hand evaluator with a plugin-style API, which I wasn't expecting from a payroll/HR company.

Questions Asked (1)

Extend a poker hand comparator by adding a method that lets callers register custom hand types via a string ID and a matching function. The main evaluation function should also accept a priority-ordered list of hand type IDs to control which registered types take precedence during comparison.

Algorithms & Data StructuresAPI & IntegrationsTechnical Trade-offs

Author's notes

The first part felt manageable, basically a registry pattern with a dict mapping type IDs to callables.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the existing comparator's design and the requirements for extensibility, then propose a registration mechanism using a map from string IDs to matching functions. For the priority-ordered list, explain how you would iterate through the list and apply each matching function in order, ensuring that custom types can override or be overridden based on the provided priority. Discuss trade-offs such as performance, API usability, and potential conflicts between custom and built-in types.

Pro tip: Emphasize the importance of a stable and predictable ordering: document that the priority list is authoritative, and consider providing a default priority list that includes built-in types so existing behavior is preserved. Also, mention that matching functions should be pure and side-effect-free to avoid subtle bugs.

1. Clarify requirements and existing design

Ask questions to understand the current comparator's API, how hand types are represented, and what 'matching function' means (e.g., returns boolean or a score). Confirm whether custom types should be able to override built-in ones and how ties are resolved.

2. Design the registration API

Propose a method like registerHandType(String id, Function<Hand, Boolean> matcher) that stores the matcher in a map. Consider thread-safety if needed, and whether to allow re-registration or removal.

3. Modify evaluation to use priority list

Change the main evaluate method to accept a List<String> of hand type IDs in priority order. Iterate through the list, look up each matcher, and return the first matching hand type. If none match, fall back to a default (e.g., high card).

4. Handle edge cases and backward compatibility

Ensure that if the priority list is empty or contains unknown IDs, the method behaves gracefully (e.g., throw exception or ignore). Provide a default priority list that includes built-in types to maintain existing behavior.

5. Discuss trade-offs and testing

Talk about performance implications (e.g., linear scan vs. caching), API usability (e.g., builder pattern for priority list), and how to test custom types and priority ordering. Mention potential conflicts if two custom types match the same hand.

Key Points to Mention

Use a Map<String, Function<Hand, Boolean>> to store registered hand types for O(1) lookup.
The priority list should be iterated in order, and the first matching hand type wins.
Provide a default priority list that includes built-in hand types to preserve backward compatibility.
Consider thread-safety if registration can happen concurrently with evaluation.
Document that matching functions should be deterministic and side-effect-free.
Discuss how to handle unknown IDs in the priority list (e.g., throw IllegalArgumentException or log a warning).

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