Explain how to understand a large codebase fast
Company: Instacart
Role: Software Engineer
Category: Software Engineering Fundamentals
Difficulty: hard
Interview Round: Technical Screen
You are given an unfamiliar, large codebase with many classes and modules. You may use an IDE (jump-to-definition, find usages, call hierarchy) and AI-assisted code search, but you have limited time.
**Task**
1. Describe a structured approach to quickly understand what the system does and how the major classes interact.
2. Explain how you would map class-to-class relationships (e.g., ownership, dependencies, call paths, data flow).
3. List the specific IDE/AI workflows you would use (and in what order).
4. Call out common pitfalls (e.g., misreading abstractions, missing runtime wiring) and how you would validate your understanding.
Assume you will be asked to present your findings after ~30–60 minutes (e.g., a short walkthrough of the main execution flow and key components).
Quick Answer: This question evaluates a candidate's ability to rapidly comprehend a large unfamiliar codebase, including identifying system behavior, mapping class-to-class relationships such as ownership and dependencies, and recognizing data and call flows.