System design interview question
"Design a shopping cart for an e-commerce site. Users add items, the cart persists across devices and sessions, prices and availability can change while items sit in the cart, and eventually they check out. 100 million users."
This is the warm-up / junior-to-mid screen in this list, and it is deceptively rich. The interesting content is not storage — it is: what happens when a cart contains data that has since changed (price, stock, the item itself), how anonymous carts merge with logged-in carts, and whether the cart reserves inventory. Candidates who treat it as "a table with user_id and item_id" miss everything interesting.
On Practick another engineer interviews you live for 60 minutes on a question from this bank. They have the full interviewer guide beside the call: the answers to your clarifying questions, the numbers to hand out, a ladder of follow-ups and a scoring rubric. You get the model solution once the session settles. It is free: interview someone for an hour and you have earned your own.
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