PRACTICE LIBRARY
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ONE ROUND, ONE NEXT STEP
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FREE REASONING EXERCISES
Original short exercises with an explanation.
01 / Reliability
Your service receives delivery notifications for customer receipts. A sender may retry the same event after a timeout, and two workers may receive it together. The receipt must be recorded once. Explain the design you would ship first.
Try this exercise02 / Data structures
A service records request timestamps in nondecreasing order. Before accepting a request at time t, it needs the count of accepted requests in the last 60 seconds. Requests exactly 60 seconds old should no longer count. Describe an efficient in-memory design for one process.
Try this exercise03 / System design
An internal dashboard reads a shared status summary. After a cached summary expires, many requests arrive together. Rebuilding the summary is expensive. A slightly stale summary is acceptable for up to 30 seconds. Explain how to keep the dashboard responsive.
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