# Implementing LFU Cache in O(1) Time: A Hands-on Breakdown

DevFeed: [Implementing LFU Cache in O(1) Time: A Hands-on Breakdown](<https://devfeed.tech/articles/implementing-lfu-cache-in-o-1-time-a-hands-on-breakdown-39586.md>)

Original publisher: [Read original article](<https://ankit-rana.com/logs/34-lfu-cache-o1-implementation/>)

Author: hello@ankit-rana.com

Published: 2026-08-02T00:00:00Z

Content type: tutorial

Language: en

Sources: [Ankit Rana | Mechanical Sympathy](<https://devfeed.tech/sources/ankit-rana-mechanical-sympathy.md>)

Topics: [Cache](<https://devfeed.tech/topics/cache.md>), [Caching](<https://devfeed.tech/topics/caching.md>), [Data structures](<https://devfeed.tech/topics/data-structures.md>), [implementation](<https://devfeed.tech/topics/implementation.md>)

Tags: [algorithms](<https://devfeed.tech/tags/algorithms.md>), [cache](<https://devfeed.tech/tags/cache.md>), [caching](<https://devfeed.tech/tags/caching.md>), [implementing](<https://devfeed.tech/tags/implementing.md>), [java](<https://devfeed.tech/tags/java.md>), [lfu](<https://devfeed.tech/tags/lfu.md>), [memory](<https://devfeed.tech/tags/memory.md>), [order](<https://devfeed.tech/tags/order.md>), [performance](<https://devfeed.tech/tags/performance.md>), [pointers](<https://devfeed.tech/tags/pointers.md>), [system-design](<https://devfeed.tech/tags/system-design.md>)

## AI overview

This tutorial explains why LRU can evict a frequently requested product during a long-tail burst, then presents an O(1) LFU cache design. It contrasts a naive O(n) eviction scan with an implementation using key-to-node and frequency-to-bucket maps, doubly linked lists, and a minFreq pointer.

## Source excerpt

LFU evicts the least frequently used key rather than the least recently used, which protects a hot key during a long-tail burst that would make LRU drop a bestseller. The naive implementation scans every key to find the minimum frequency, which is O(n) per eviction. The O(1) version inverts the index: a key-to-node map, a frequency-to-bucket map of doubly linked lists, and a minFreq pointer.