Lyft·Software Engineer·Technical Phone Screen·Intermediate

IntermediatePrefer not to say

Jun 2026Remote

Summary

Lyft SWE coding round last month. The problem itself wasn't bad but the test case requirement blindsided me and I ran out of time before getting anything to actually execute.

Questions Asked (1)

Implement a key-value store that parses and executes command strings line by line, where each line can be a standalone command, a command with a key and value, or a command with a single value. You also need to write your own test cases and run them.

Algorithms & Data StructuresTechnical Trade-offs

Author's notes

The KV store part I'd seen before and felt fine about.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the command syntax and expected behaviors, then design a modular parser and executor with a clear data structure for storage. Implement the solution with extensibility in mind, and write comprehensive tests covering edge cases and command variations.

Pro tip: Demonstrate test-driven development by writing tests before implementation, and discuss how you would handle concurrency and persistence if the store needed to scale.

1. Clarify Requirements

Ask questions to understand the exact command formats, expected operations (e.g., SET, GET, DELETE), and any constraints like case sensitivity or error handling.

2. Design the Architecture

Outline a modular design with a parser to tokenize lines and an executor to perform operations on an in-memory data structure like a hash map.

3. Implement Core Logic

Code the parser to handle different line structures and the executor to manipulate the key-value store, ensuring clean separation of concerns.

4. Write Test Cases

Develop unit tests for parsing and execution, covering valid commands, invalid inputs, edge cases (empty lines, extra spaces), and command sequences.

5. Run and Iterate

Execute tests, debug failures, and refine the implementation. Discuss potential optimizations and trade-offs for scalability.

Key Points to Mention

Command parsing techniques (e.g., splitting by whitespace, handling quoted values)
Data structure choice (hash map for O(1) average time complexity)
Error handling for malformed commands and unknown operations
Test coverage including edge cases and command sequences
Extensibility for adding new commands
Trade-offs between simplicity and features like persistence or concurrency

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