Art of Codeartofcode
Lesson 11 of 21

1. How to Approach a Design Question

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The picture to keep in your head
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1.1 What is a system design interview, and what isn't it?
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1.2 What is the interviewer actually scoring?
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1.3 What's the step-by-step framework?
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1.4 How do you manage a 45-minute round?
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1.5 What questions should you ask first?
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1.6 What's the difference between functional and non-functional requirements?
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1.7 What's an API, and why define it before drawing boxes?
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1.8 How do you sketch the data model?
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1.9 What does a good high-level design look like?
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1.10 How do you choose what to deep dive into?
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1.11 How do you talk about trade-offs?
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1.12 What if you get stuck or don't know something?
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1.13 What are the most common mistakes?
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1.14 What does the bar look like: fresher vs SDE-2?
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Memory card and where the analogy breaks
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Practice: five levels
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Interview questions
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Solutions
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Sources
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Code lab
1. How to Approach a Design Question

1.10 How do you choose what to deep dive into?

3 min read+10 XP

At the architect's desk: After the floor plan, the architect zooms in. Not on the paint colour, but on the part most likely to fail or most expensive to get wrong: the staircase in a narrow house, the beams in an earthquake zone.

In the interview: The deep dive is where you take one part of the design and solve it properly. Pick the part that's hardest or riskiest given this problem's numbers. Good signals:

  • The bottleneck: the component under the most load. (URL shortener: thousands of redirects per second hitting storage.)
  • The tricky correctness problem: where it's easy to be subtly wrong. (URL shortener: two links must never get the same code.)
  • The thing the interviewer keeps asking about. That's a hint. Follow it.

A strong move: offer a choice. "I think the two hard parts are generating unique codes and keeping redirects fast. Which would you like me to go deeper on?" It shows you see both, and it lets the interviewer steer you to what they score.

Memory code: "Dive where it hurts." Go deep on the bottleneck or the tricky part, not on the paint.