The naive solution comes to mind fast, a simple frequency map, but then they ask about O(1) and you realize a sorted structure won't cut it.
Start by clarifying requirements and constraints, then propose a design using a combination of a hash map and a doubly linked list of frequency nodes, each containing a doubly linked list of keys. Explain how this achieves O(1) average time for get and put, and handle edge cases like updating frequency and eviction with LRU tiebreaking.
Pro tip: Mention that you would use a sentinel head and tail in the frequency list to simplify edge cases, and discuss how to handle capacity zero or one. Also, note that the design can be extended to support concurrency with fine-grained locking if needed.
Ask about cache capacity, expected operations, and whether thread safety is required. Confirm that O(1) average time is needed for both get and put.
Propose a hash map mapping keys to nodes, and a doubly linked list of frequency nodes. Each frequency node contains a set of keys implemented as a doubly linked list to maintain LRU order.
Detail how get and put work: for get, move the key to the next frequency node; for put, insert or update the key and handle eviction when capacity is exceeded.
Describe eviction: remove the least frequently used key from the lowest frequency node, and if that node becomes empty, remove it. Use LRU tiebreaking by removing the least recently used key from that node.
Discuss time and space complexity, and cover edge cases like capacity 0, updating existing keys, and frequency updates. Mention potential optimizations or concurrency considerations.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.