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coreweave·Software Engineer·Technical Phone Screen·Senior

SeniorPrefer not to say
May 2026Remote

Summary

Coreweave software engineer interview with a system design question around building a predicate evaluation engine. Not a typical LeetCode grind, more of a design-your-own-mini-language problem which I wasn't expecting.

Questions Asked (1)

Q1

Design a data structure that can represent and evaluate boolean predicate expressions like `abc > 5 and (test < 8 or team > 9)`, supporting comparisons, logical operators, parentheses, and evaluation against a variable dictionary.

System DesignAlgorithms & Data StructuresTechnical Trade-offs
Author's notes

I spent the first few minutes just staring at the problem trying to figure out if they wanted a parser or a data structure or both.

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AI HintsAI Generated

Suggested Approach

Start by clarifying requirements and constraints, then propose a design using an abstract syntax tree (AST) with nodes for comparisons and logical operators, and a recursive evaluator. Discuss parsing (e.g., recursive descent or shunting-yard) and evaluation strategies, including short-circuiting and error handling.

Pro tip: Mention that you would separate parsing from evaluation to allow caching of parsed expressions and reuse across multiple evaluations, which is crucial for performance in high-throughput systems.

1. Clarify Requirements

Ask about supported operators, data types, expected expression complexity, and performance needs. Confirm whether expressions are provided as strings and evaluated against a dictionary of variables.

2. Design the AST

Define node types: comparison nodes (e.g., >, <, ==) with left/right operands, logical nodes (and, or, not) with child nodes, and leaf nodes for variables and literals. This tree structure naturally handles parentheses and operator precedence.

3. Implement Parsing

Use a recursive descent parser or shunting-yard algorithm to convert the infix expression string into an AST, respecting operator precedence and parentheses. Tokenize the input first.

4. Implement Evaluation

Write a recursive evaluator that traverses the AST, looks up variable values in the provided dictionary, and computes boolean results. Implement short-circuit evaluation for logical operators to avoid unnecessary computations.

5. Discuss Trade-offs and Extensions

Compare design choices: AST vs. direct interpretation, recursive descent vs. shunting-yard, and handling of errors. Mention possible optimizations like constant folding, caching, or compiling to bytecode.

Key Points to Mention

  • Abstract Syntax Tree (AST) as the core data structure for representing expressions.
  • Recursive descent parsing for handling operator precedence and parentheses.
  • Short-circuit evaluation for logical operators (and, or) to improve performance.
  • Error handling for invalid expressions, type mismatches, or missing variables.
  • Separation of parsing and evaluation to enable caching and reuse.
  • Trade-offs between simplicity (e.g., direct evaluation) and flexibility (e.g., AST with visitors).

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