Art of Codeartofcode
Lesson 20 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

Sources

3 min read+10 XP

Source notes

  • Round length (45 to 60 minutes) and the step split are typical practice, not a fixed standard. They vary by company and level.
  • The "5 Cs" are this book's summary of commonly used signals (requirements, design, depth, trade-offs, communication), not any one company's official rubric.
  • 301 (Moved Permanently) responses may be cached by browsers by default; 302 (Found) responses are not cached unless headers say so: HTTP Semantics, RFC 9110, sections 15.4.2 and 15.4.3.
  • Level 2 numbers, base62 code lengths (62⁵ = 916,132,832; 62⁶ = 56,800,235,584) and the 1.8% collision chance at 1 billion links (10⁹ ÷ 62⁶) were computed 2026-10-05.
  • Level 3 and Level 4 code: tested 2026-10-05 (code/ch01_url_shortener.py, all checks pass).
  • All traffic numbers in this chapter are interview assumptions, not real figures for any company.