In an LRU cache implemented with a hashmap and a doubly linked list, what is the meaning of the head and tail in the recency order?

• A. Head is the most recently used, tail is the least recently used
• B. Head is the least recently used, tail is the most recently used
• C. Head and tail roles are interchangeable
• D. Only tail tracks recency; head is dummy

Answer: (A)

In this LRU setup, the recency order is reflected by the doubly linked list: the item at the head is the most recently used, and the item at the tail is the least recently used. When you access or insert something, you move its node to the head, marking it as MRU. When you need to evict, you remove the node at the tail, which is the LRU. The hashmap gives O(1) access to the node, and the doubly linked list lets you move or remove nodes in constant time without traversal, keeping the whole operation efficient. If the head were the least recently used or if both ends could swap roles, you’d lose a clear, consistent way to perform updates and eviction in constant time.