Art of Codeartofcode
Lesson 1 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

The picture to keep in your head

3 min read+10 XP

Every question below is answered twice: first at the architect's desk, so you can picture it, then in the interview, so you know exactly what to do. Each answer ends with a memory code to lock it in.

The picture to keep in your head

A family walks into an architect's office and says, "Build us a house." A bad architect starts drawing right away. A good one puts the pencil down and asks: how many people live here? What's the budget? One floor or two? Any elderly parents who can't climb stairs? Only then does she size it, plan the doors, draw the floor plan, zoom into the tricky staircase, and walk the family through why every choice was made.

A system design interview is exactly this. The interviewer says "Design a URL shortener." Your job is to be the good architect.

Our running example: a URL shortener like bit.ly. You give it a long link, it gives you a short one, and anyone who clicks the short one lands on the long one. (You'll design it end to end in Chapter 31. Here we only use it to practise the approach.)

At the architect's deskIn the interview
The family's wish: "build us a house"The prompt: "design a URL shortener"
Asking who lives here, budget, floorsClarifying questions, requirements
4 people or 400?Estimates: users, requests per second, storage
Doors and what passes through themThe API
The store room and what's kept in itThe data model
The floor planThe high-level design
Zooming into the tricky staircaseThe deep dive
Walking the family through each choiceTrade-offs and wrap-up

the architect's process, mapped step by step to the interview.

Figure: the architect's process, mapped step by step to the interview. Nobody draws before they know who the building is for.