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Classic question but I still fumbled the doubly linked list part for a minute.
Clarify the requirements and constraints, then propose a design using a hash map for O(1) access and a doubly linked list for O(1) eviction. Walk through the implementation details, including edge cases, and analyze time and space complexity.
Pro tip: Mention that this is a classic system design question and that you would consider thread-safety if the cache is used in a concurrent environment, showing awareness of real-world usage.
Ask about cache capacity, expected operations, and whether thread-safety is needed. Confirm that get and put must be O(1).
Explain that a hash map provides O(1) access to nodes, and a doubly linked list maintains recency order for O(1) updates and evictions.
Describe how get moves the accessed node to the front, and put adds or updates a node, evicting the least recently used (tail) when capacity is exceeded.
Discuss handling of capacity 0 or 1, updating existing keys, and ensuring the list and map stay in sync.
Conclude that both operations are O(1) time and O(capacity) space, and mention potential optimizations like using a sentinel head/tail.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.