Number of Recent Calls
A easy-tier problem at 77% community acceptance, tagged with Design, Queue, Data Stream. Reported in interviews at Databricks and 4 others.
Number of Recent Calls is an easy design problem that asks you to build a data structure tracking function calls within a time window. Databricks, Affirm, Roblox, Bloomberg, and Yandex have all asked it. The acceptance rate is 77%, which means most candidates solve it, but the trap is overcomplicating the solution or picking the wrong underlying data structure. If you haven't seen this pattern before and it lands in your OA, StealthCoder surfaces the working approach instantly, invisible to the proctor.
Companies that ask "Number of Recent Calls"
Number of Recent Calls is the kind of problem that decides whether you pass. StealthCoder reads the problem on screen and surfaces a working solution in under 2 seconds. Invisible to screen share. The proctor sees nothing. Built by a senior engineer who knows the OA is theater. This is the script.
Get StealthCoderThe problem forces you to think about data stream tracking and eviction policy. The naive approach is to store all calls and scan the entire list on each query, which tanks performance under load. The real pattern is a Queue paired with a sliding window: push the new call timestamp, evict old timestamps outside the window, return the size. This is a textbook Design and Data Stream problem that tests whether you pick the right tool for the job. Most candidates either overthink it or lock into a slow solution early. StealthCoder is your hedge if the pattern doesn't click during the live assessment.
Pattern tags
You know the problem.
Make sure you actually pass it.
Number of Recent Calls recycles across companies for a reason. It's easy-tier, and most candidates blank under the timer. StealthCoder is the hedge: an AI overlay invisible during screen share. It reads the problem and surfaces a working solution in under 2 seconds. Built by a senior engineer who knows the OA is theater. This is the script. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Number of Recent Calls interview FAQ
Is this problem actually asked at real companies?+
Yes. Five confirmed companies report it, including Databricks and Bloomberg. It's a lower-frequency ask overall, but it shows up in system-design rounds where interviewers want to see if you understand data structures and time-based constraints.
What's the trick that people miss?+
Candidates often store all timestamps and filter them on each query, which is O(n) per call. The pattern is a Queue with lazy eviction: pop expired timestamps as you add new ones. It's O(1) amortized and forces you to think about sliding windows.
Is this a real design question or just a coding problem?+
It sits at the boundary. The problem statement is minimal, but the design challenge is choosing the right data structure. You're expected to know Queue semantics and how to manage time-based state efficiently in a stream.
How does this relate to the other Design and Queue topics?+
This is a foundational data-stream problem. It teaches queue-based state management under a time constraint, a pattern you'll see in rate limiters, event processors, and real-time analytics systems.
If I blank on the approach during an OA, what's the fallback?+
StealthCoder reads the problem, identifies the sliding-window queue pattern, and surfaces a correct solution in seconds. You paste it, move on, and keep your assessment score intact.
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