LRU Cache: Design and Implementation

Design problems test your ability to create data structures and classes that support specific operations with required time and space complexities. For this problem, we need to carefully choose the underlying data structures to meet the performance requirements for each operation. A common pattern is combining multiple data structures: for example, an LRU cache uses a hash map for O(1) lookups combined with a doubly linked list for O(1) insertion and deletion at both ends. When designing data structures for interviews, start by listing all required operations and their target time complexities. Then consider which primitive data structures (arrays, linked lists, hash maps, heaps, trees) can provide those complexities. Often, the optimal design combines two or more structures where each handles different aspects of the problem. Think carefully about edge cases: what happens when the structure is empty, full, or contains duplicate elements. Consider thread safety if the interviewer asks about concurrent access. Implement clean interfaces with well-named methods and handle error cases gracefully. Testing your design with example inputs during the interview demonstrates thoroughness. Common design problems include LRU and LFU caches, min stacks, queues using stacks, random access data structures, and time-based key-value stores.