## Expiring Counter (sliding time window) Design and implement an **expiring counter** that counts events in a recent time window. ### Requirements - You are given a fixed window size `W` in **seconds** when constructing the counter. - Support two operations: 1. `inc(timestamp, delta=1)`: record `delta` events occurring at integer time `timestamp` (in seconds). 2. `get(timestamp) -> int`: return the total number of events recorded in the **inclusive** time range: \[ [timestamp - W + 1,\; timestamp] \] ### Assumptions / clarifications (state and use in your solution) - Timestamps are integer seconds. - You may assume calls arrive with **non-decreasing timestamps** (typical for streaming counters). If you choose not to assume this, explain how you would handle out-of-order inputs. ### Constraints / goals - Aim for efficient time and space usage: roughly **O(1) amortized** per operation and memory proportional to the window. ### Follow-up If `inc()` can be called up to **1,000,000 times per second**, how would you modify the design to reduce memory and CPU overhead (e.g., batching/aggregating within each second)?