gulangyuzzz / lfucache

O(1) time implementation of LFU cache in JAVA

LFU cache

A data structure for Least Frequently Used (LFU) cache. Supports following operations: get and set.

get(key) - Get the value of the key if the key exists in the cache, otherwise return null

set(key, value) - Set or insert the value if the key is not already present. When the cache reaches its capacity, it should invalidate the least frequently used item before inserting a new item. when there is a tie (i.e., two or more keys that have the same frequency), the least recently used key would be evicted.

// Get procedure // 1. Get LFUCacheEntry reference from HashMap // 2. Find Frequency Node from the Entry Node // 3. Remove Entry Node from Frequency Node list and add it to next freuquency Node // list // a. If New frequency Node doesn't exist, create a new one and add its entry // into frequency Node set // b. If Previous Frequency Node list is now empty remove that frequency Node

// Set procedure // 1. If same key already exists // Remove that LFUCacheEntry from Frequency Node & remove frequnecy Node if its // Empty // Remove that key & corresponding LFUCacheEntry from HashMap // If Cache is full remove very first entry from very first frequency Node in list

// 2. Add New LFUCacheEntry into HashMap // 3. Add this new Entry into Frequency Node of frequency 1 // a. Create if such a node doesn't already exist