Implement a Capacity-Bounded Cache

Implement an in-memory key-value cache with a fixed capacity. The cache must support the following operations in constant time on average: - `get(key)`: Return the value associated with `key` if it exists; otherwise return `-1`. - `put(key, value)`: Insert or update the value for `key`. If inserting a new key would exceed the cache capacity, evict the item that has been unused for the longest time. Accessing or updating a key makes it the most recently used item. You should be prepared to explain the underlying data structures, especially how a hash map and a doubly linked list can be combined to support both fast lookup and fast eviction.