Get Active Requests Count
Reported by candidates from Amazon's online assessment. Pattern, common pitfall, and the honest play if you blank under the timer.
Amazon asked this in August 2024, and it's a deceptive problem. At first glance it sounds like a basic counter. You're tracking active requests, probably over a time window or lifecycle. The trick is usually in how you define 'active' (concurrent at a point in time, or within a window?) and whether you need to handle updates or queries efficiently. If you blank on the approach, StealthCoder will spot the pattern and give you the working skeleton in seconds.
Pattern and pitfall
This problem typically boils down to either event processing with timestamps or a data structure that tracks state. If requests have start/end times, you're looking at an interval overlap problem, often solved with sorting events and a sweep line or a heap. If it's a live counter that increments/decrements, you need a concurrent-safe design. The pitfall most candidates hit is not clarifying the input format upfront: are you given a list of request objects with timestamps, or a stream of add/remove operations? StealthCoder on your second monitor will help you identify which pattern applies before you code yourself into a corner.
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Get Active Requests Count FAQ
Is this about counting overlapping time intervals?+
Likely. If requests have start and end times, you sort events (start/end markers) and sweep left to right, tracking the current count. Peak active requests is the max count seen. That's the classic interval overlap trick.
Do I need to optimize for multiple queries, or one final answer?+
Ask yourself: is the input a single list of requests, or does the problem ask you to handle many 'how many active at time T' queries? If queries, a sorted list plus binary search or a segment tree. If single answer, a sweep line is enough.
What if the problem is about a live counter, not time windows?+
Then you're tracking concurrent requests via add/remove operations. A simple integer counter works, but think about thread safety if the problem hints at concurrency. Atomic operations or locks might be the real question.
How hard is this really for Amazon in August 2024?+
Medium. It's testing whether you can model the problem correctly and pick the right data structure. The sorting and sweep line pattern is not trivial but well-known. Most failures are from misreading the input format.
Can I prepare for this in 48 hours?+
Yes. Drill interval overlap, event-based sorting, and heap-based approaches. Understand merge intervals and the meeting rooms problems on LeetCode. That covers 90 percent of the space.