1. How to Approach a Design Question
1
The picture to keep in your head2
1.1 What is a system design interview, and what isn't it?3
1.2 What is the interviewer actually scoring?4
1.3 What's the step-by-step framework?5
1.4 How do you manage a 45-minute round?6
1.5 What questions should you ask first?7
1.6 What's the difference between functional and non-functional requirements?8
1.7 What's an API, and why define it before drawing boxes?9
1.8 How do you sketch the data model?10
1.9 What does a good high-level design look like?11
1.10 How do you choose what to deep dive into?12
1.11 How do you talk about trade-offs?13
1.12 What if you get stuck or don't know something?14
1.13 What are the most common mistakes?15
1.14 What does the bar look like: fresher vs SDE-2?16
Memory card and where the analogy breaks17
Practice: five levels18
Interview questions19
Solutions20
Sources21
Code lab1. How to Approach a Design Question
1.13 What are the most common mistakes?
3 min read+10 XP
At the architect's desk: The classic bad architect draws a 50-floor tower for a family of four: impressive, expensive, and wrong for them.
In the interview:
Figure: weak vs strong first five minutes. Same knowledge, very different score.
| Mistake | Why it hurts | Instead |
|---|---|---|
| Drawing before asking | You solve the wrong problem | SCALE questions first |
| Over-engineering | Microservices and Kafka for 1,000 users look like you can't judge scale | Simplest design that meets the numbers |
| Buzzwords without reasons | "We'll use Kafka" with no why scores nothing | Because, Cost, Unless |
| Going silent | The interviewer can't score what they can't hear | Think out loud |
| Spending all the time on one box | No complete design at the end | Watch the 5-5-10-10-10-5 split |
| Ignoring hints | The interviewer was steering you somewhere | When they ask twice, go there |
| No wrap-up | You never show you know the weak spots | Name the bottleneck and what you'd improve |
Memory code: "Don't build a skyscraper for a family of four." Fit the design to the numbers, not to your favourite tools.