Ziphq·Software Engineer·Technical Phone Screen·Senior

SeniorPrefer not to say

Jun 2026Remote

Summary

Ziphq software engineering interview that was basically one big design problem: build a composable condition evaluator from scratch. The kind of question that sounds clean on paper but has a lot of surface area once you start implementing it.

Questions Asked (1)

Design and implement a composable condition evaluation system where conditions are represented as an AST with atomic predicates (equals, greater-than, contains) and composite nodes (And, Or, Not), supporting programmatic construction, an evaluate(record) method, error handling for malformed inputs, and extensibility for new predicate types.

System DesignAlgorithms & Data StructuresTechnical Trade-offs

Author's notes

I started with the class hierarchy and felt pretty good about it.

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AI HintsAI Generated

Suggested Approach

Start by clarifying requirements and defining the AST node types, then sketch the class hierarchy with a common evaluate interface. Discuss how to handle errors and extensibility, and walk through an example evaluation. Finally, mention trade-offs like performance and testability.

Pro tip: Emphasize the use of the Composite and Interpreter patterns to make the system extensible and maintainable. Also, highlight the importance of separating parsing/construction from evaluation to keep the design clean.

1. Clarify Requirements and Scope

Ask questions to understand the expected input format, error handling needs, and extensibility requirements. Confirm whether conditions are constructed programmatically or parsed from a DSL.

2. Design the AST and Node Hierarchy

Define an abstract Node class with an evaluate(record) method. Create atomic predicate nodes (Equals, GreaterThan, Contains) and composite nodes (And, Or, Not) that hold child nodes.

3. Implement Evaluation and Error Handling

Implement evaluate for each node type, ensuring type checks and throwing meaningful exceptions for malformed inputs. Use short-circuit evaluation for And/Or.

4. Ensure Extensibility

Design the system so new predicate types can be added without modifying existing code, e.g., via a registry or by subclassing. Discuss how to handle new composite nodes.

5. Discuss Trade-offs and Testing

Mention performance considerations (e.g., caching, short-circuiting) and how to test each node type and the overall system. Compare alternative designs like using a functional approach.

Key Points to Mention

Use of Composite and Interpreter design patterns for AST representation and evaluation.
Separation of concerns: construction (builder/parser) vs. evaluation logic.
Error handling strategies: validation at construction time vs. evaluation time, and custom exceptions.
Extensibility mechanisms: plugin architecture, registry, or subclassing for new predicates.
Performance optimizations: short-circuit evaluation, caching, and avoiding unnecessary record field access.
Testing approach: unit tests for each node type, integration tests for complex conditions, and property-based testing.

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