Explain LRU caching and its purpose.

Explain LRU caching and its purpose.

• A. Evict the least recently used item when the cache is full.
• B. Evict the most recently used item.
• C. Evict a random item.
• D. Never evict items; cache grows indefinitely.

Answer: (A)

LRU caching uses recency as the signal for what to evict when space runs out. The idea is simple: keep a small set of items that you’re most likely to need again soon in fast-access memory, so future requests can be served quickly without going to the slower underlying store. Every time you access an item, you mark it as most recently used. If the item isn’t in the cache (a miss), you fetch it and insert it; if the cache is full, you remove the item that hasn’t been used for the longest time—the least recently used. This mirrors the intuition that recently used data is more likely to be needed again soon than data that hasn’t been touched in a while.

In practice, LRU is often implemented with a hash map for quick lookup and a doubly linked list to track order of use, so moving an item to the most-recent spot and evicting the least-recent one happen in constant time. The purpose is to maximize cache hits and minimize latency by keeping hot, frequently accessed data in fast memory, rather than letting the cache grow indefinitely or evict items that are still useful.