LRU Cache
Design an LRU Cache with O(1) get and put operations. Think about: What data structures enable O(1) access and ordering? Hint: Combine a hash map with a doubly linked list. Example: LRUCache(2) put(1, 1), put(2, 2) get(1) → 1 put(3, 3) # evicts key 2 get(2) → -1
Design a cache that evicts the least recently used item when full. It's one of the few problems that tests both data structure intuition and clean API design. Interviewers love it because it reveals whether you can combine a hash map with a linked list to get O(1) operations. This pattern shows up constantly in systems design.
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