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Advanced Topic 42 of 52 Data Structures

LRU Cache Structure

Hash map plus linked list evicting least recently used entries.

How it works

An LRU cache combines a hash map, mapping keys to list nodes, with a doubly linked list ordered by recency. Accessing a key moves its node to the front; when the cache is full, the node at the tail, the least recently used one, is evicted. Both get and put run in O(1) time, which is why this pairing is the standard design.

Step-by-step walkthrough

  1. get(k) finds the node in the hash map in O(1).
  2. The node is moved to the front of the linked list as most recently used.
  3. put(k) with a full cache evicts the tail node.
  4. The evicted key is removed from the map too.
  5. The new key is inserted at the front.

Where it is used

Web browsers, database buffer pools, operating-system page caches, CDN edge servers and memoization layers use LRU eviction. Libraries offer ready-made implementations.

Common pitfall

Forgetting to update recency on reads, or leaving a stale map entry after eviction, breaks correctness. Not thread-safe by default: concurrent access needs locks. Scans of large datasets can flush useful entries, so consider variants such as LRU-K or 2Q.

Where it fits in the course

LRU Cache Structure is topic 42 of 52 in Data Structures, rated Advanced. It follows Quadtrees. The next topic is Circular Buffer.

Practice and explore

How to study this topic

  1. Read the explanation above and restate the definition in your own words.
  2. Open the interactive lesson and answer its mini quiz.
  3. Read the common pitfall, then write a short example that avoids it.
  4. Check your understanding in the Data Structures quiz, and revisit the topic if you miss a question.

Frequently asked questions

What is LRU Cache Structure?
Hash map plus linked list evicting least recently used entries. It belongs to Data Structures and is an advanced-level topic.
Where do people use LRU Cache Structure?
Web browsers, database buffer pools, operating-system page caches, CDN edge servers and memoization layers use LRU eviction.
What is the most common mistake with LRU Cache Structure?
Forgetting to update recency on reads, or leaving a stale map entry after eviction, breaks correctness.
What should I learn before this topic?
Start with Quadtrees, the topic just before it in Data Structures.
How can I practice it?
Answer the mini quiz in the interactive lesson, then take the Data Structures quiz.
Is LRU Cache Structure hard to learn?
It is an Advanced topic. Expect to read the explanation more than once and to connect it with earlier topics. Working through a small example by hand helps most.
How long does it take to learn LRU Cache Structure?
Most learners can read the explanation and finish the interactive lesson in under an hour. Fluency comes from applying the idea, so plan a few short practice sessions with the quiz.
Which topics are related to LRU Cache Structure?
Quadtrees, Circular Buffer, KD-Trees are closely connected. The full list is in the related topics section of this page.
What should I study after LRU Cache Structure?
Continue with Circular Buffer, the next topic in Data Structures.

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