Implement the complete LRU cache with operations.
Implementation checklist: - Initialize dummy head and tail, link them together - Hash map stores key → node pointers - Each node stores key, value, prev, next - get: lookup, move to front if found - put: handle update vs. insert, check capacity Common bugs: - Forgetting to store the key in the node (needed for eviction) - Not linking head and tail in constructor - Off-by-one in capacity check This problem appears constantly in interviews because it tests both data structure knowledge and implementation skill.
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