I learned just about everything I needed to learn about system design to ace a mid-level SD interview in about 10 days for free. Here’s how I did it:
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Day 1-7: Go to HelloInterview and go through all of their free resources (This is not sponsored or anything. This specific tool is really that good). You may need to repeat each module to make sure you truly understand how it fits into the entire system as a whole. I actually do think purchasing a subscription to HelloInterview is an absolute steal given the quality of their content but it’s 100% not necessary.
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Day 8-9: Using the AI tool of your choice (I use Claude), ask it to interview you on each specific topic in system design. Ask it to take note of everything you didn’t quite get and generate new questions on those topics until you have sufficiently covered all topics.
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Day 10: Have the AI ask you to design a full system that might show up on a real interview and give your answers in as many details as you can. Repeat this step until you really feel like you have the framework and the concepts down completely.
Does this mean you will absolutely be an expert in all things system design? No.
However, it will make you more knowledgeable than most other junior to mid-level candidates.