Design a rolling five-minute hit counter

Q: Design a rolling five-minute hit counter

This is a Coding & Algorithms interview question from Apple for Software Engineer roles. View the full question and solution on PracHub.

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Question

Design an in-memory hit counter that supports: (

recordHit(timestamp) to log an event, and (
getCountLast5Minutes(now) to return the number of events that occurred in the past 300 seconds. Assume timestamps are integer seconds and non-decreasing across calls. Explain how to expire outdated events efficiently without storing every hit individually, detail your data-structure choices and time/space trade-offs, target O(
amortized per operation with O(
space, and implement the API with unit tests.

Design a rolling five-minute hit counter

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