Classic question but the pressure of doing it live always makes the doubly linked list part messier than it looks on paper.
Start by clarifying the requirements: capacity, thread-safety, and expected time complexity. Then propose a hash map combined with a doubly linked list to achieve O(1) get and put operations, and walk through the implementation details and edge cases.
Pro tip: Mention that you would use a doubly linked list with sentinel head and tail nodes to simplify edge cases, and discuss how to make it thread-safe if needed (e.g., using synchronized or ConcurrentHashMap with a lock).
Ask about capacity limits, concurrency requirements, and whether the cache should be thread-safe. Confirm that get and put should both be O(1).
Propose a hash map for O(1) key lookup and a doubly linked list to maintain access order. Explain that the map stores key -> node, and the list keeps most recently used at the front.
Describe get: if key exists, move node to front and return value; else return -1. Describe put: if key exists, update value and move to front; else add new node to front, and if capacity exceeded, remove least recently used (tail) node and delete from map.
Discuss edge cases: capacity 0 or 1, updating existing key, and removing the least recently used node correctly. Mention using sentinel nodes to avoid null checks.
State that both operations are O(1) time and O(capacity) space. If thread-safety is required, discuss using synchronized methods or a concurrent approach with fine-grained locking.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.