What is the Sliding Window technique? Give a use case.

0-2 years experience

1. 1Given an array of integers, how would you find the length of the longest subarray whose sum is less than or equal to K using a sliding window?
2. 2If you need the smallest substring that contains all characters of a target set, how would you apply a sliding window to solve it?
3. 3What happens to a sliding‑window approach when the array includes negative numbers?

2-5 years experience

1. 1We need a rate limiter that allows at most N requests per minute per user. How would you implement it with a sliding window and what edge cases would you watch for?
2. 2Your moving‑average feature for sensor readings is showing latency spikes after deployment. Walk me through how you’d debug the sliding‑window implementation and improve performance.
3. 3When computing the maximum number of concurrent sessions in any 5‑minute window from logs, why might a naive sliding window be insufficient, and what trade‑offs would you consider?

5-8 years experience

1. 1Design a high‑throughput service that computes rolling aggregates (sum, max) over a sliding time window for millions of events per second. Which data structures and partitioning strategies would you choose, and how would you handle out‑of‑order events?
2. 2Our distributed cache uses a sliding‑window expiration policy, but we see memory leaks when many keys have overlapping windows. How would you redesign the expiration mechanism to be accurate and scalable?
3. 3How would you test the correctness and performance of a sliding‑window implementation under burst traffic conditions?

8+ years experience

1. 1We are migrating a legacy monolith that uses ad‑hoc sliding‑window loops for analytics to a microservices architecture with a stream‑processing platform (e.g., Flink or Kafka Streams). What architectural considerations and migration steps would you propose to preserve correctness and latency?
2. 2Across multiple teams, some services use count‑based windows while others use time‑based windows. How would you establish a unified sliding‑window framework that balances flexibility, operational overhead, and observability?
3. 3Discuss the long‑term maintenance implications of embedding sliding‑window logic directly in business code versus abstracting it into a shared library or service.