←ENG-DSA-065Real-time API Analytics (Queue/Deque)
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Real-time API Analytics (Queue/Deque)

CompaniesStripe, Datadog
Est. Time~25 min
LevelMid
DesignQueueStreaming
🚨 P0 Incident
StripeDatadog

API Gateways like Stripe must display "Requests in the last 5 minutes" on their analytics dashboards. Storing every timestamp forever causes Out-Of-Memory crashes. Using a sliding queue dynamically prunes data older than 300 seconds, maintaining a strict upper memory bound.

📥 Assigned to:You — Mid Engineer
Your Task

Design a HitCounter class that tracks the number of API hits. It should support `hit(timestamp)` to record a hit, and `get_hits(timestamp)` to return the total hits in the past 5 minutes (300 seconds). Timestamps are strictly increasing.

⏱ Time: O(1) amortized💾 Space: O(W) where W is max hits in 300 seconds
Example 1
Input:  hit(1), hit(2), get_hits(4)
Output: 2
Example 2
Input:  hit(1), get_hits(300), get_hits(301)
Output: 1 at 300, 0 at 301
🔒 +3 hidden test cases — revealed on Submit
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