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Full LRU/FIFO Cache Implementation in Golang

It should support Set and Get Operation, O(1) Time Complexity for both Set and Get.

Here is the full working code in go programming language if anyone is interested.

doublylinklist.go

package main

import "fmt"

type node struct {
	key   string
	value string
	prev  *node
	next  *node
}

type doublyLinkedList struct {
	len  int
	tail *node
	head *node
}

func initDoublyList() *doublyLinkedList {
	return &doublyLinkedList{}
}

func (d *doublyLinkedList) AddToFront(key, value string) {
	newNode := &node{
		key:   key,
		value: value,
	}
	if d.head == nil {
		d.head = newNode
		d.tail = newNode
	} else {
		newNode.next = d.head
		d.head.prev = newNode
		d.head = newNode
	}
	d.len++
	return
}

func (d *doublyLinkedList) RemoveFromFront() {
	if d.head == nil {
		return
	} else if d.head == d.tail {
		d.head = nil
		d.tail = nil
	} else {
		d.head = d.head.next
	}
	d.len--
}

func (d *doublyLinkedList) AddToEnd(node *node) {
	newNode := node
	if d.head == nil {
		d.head = newNode
		d.tail = newNode
	} else {
		currentNode := d.head
		for currentNode.next != nil {
			currentNode = currentNode.next
		}
		newNode.prev = currentNode
		currentNode.next = newNode
		d.tail = newNode
	}
	d.len++
}
func (d *doublyLinkedList) Front() *node {
	return d.head
}

func (d *doublyLinkedList) MoveNodeToEnd(node *node) {
	prev := node.prev
	next := node.next

	if prev != nil {
		prev.next = next
	}

	if next != nil {
		next.prev = prev
	}
	if d.tail == node {
		d.tail = prev
	}
	if d.head == node {
		d.head = next
	}
	node.next = nil
	node.prev = nil
	d.len--
	d.AddToEnd(node)
}

func (d *doublyLinkedList) TraverseForward() error {
	if d.head == nil {
		return fmt.Errorf("TraverseError: List is empty")
	}
	temp := d.head
	for temp != nil {
		fmt.Printf("key = %v, value = %v, prev = %v, next = %v\n", temp.key, temp.value, temp.prev, temp.next)
		temp = temp.next
	}
	fmt.Println()
	return nil
}

func (d *doublyLinkedList) Size() int {
	return d.len
}

evictionAlgorithm.go

package main

type evictionAlgo interface {
	evict(c *Cache) string
	get(node *node, c *Cache)
	set(node *node, c *Cache)
	set_overwrite(node *node, value string, c *Cache)
}

func createEvictioAlgo(algoType string) evictionAlgo {
	if algoType == "fifo" {
		return &fifo{}
	} else if algoType == "lru" {
		return &lru{}
	}

	return nil
}

lru.go

package main

import "fmt"

type lru struct {
}

func (l *lru) evict(c *Cache) string {
	key := c.doublyLinkedList.Front().key
	fmt.Printf("Evicting by lru strtegy. Evicted Node Key: %s: ", key)
	c.doublyLinkedList.RemoveFromFront()
	return key
}

func (l *lru) get(node *node, c *Cache) {
	fmt.Println("Shuffling doubly linked list due to get operation")
	c.doublyLinkedList.MoveNodeToEnd(node)
}

func (l *lru) set(node *node, c *Cache) {
	fmt.Println("Shuffling doubly linked list due to set operation")
	c.doublyLinkedList.AddToEnd(node)
}

func (l *lru) set_overwrite(node *node, value string, c *Cache) {
	fmt.Println("Shuffling doubly linked list due to set_overwrite operation")
	node.value = value
	c.doublyLinkedList.MoveNodeToEnd(node)
}

fifo.go

package main

import "fmt"

type fifo struct {
}

func (l *fifo) evict(c *Cache) string {
	fmt.Println("Evicting by fifo strtegy")
	key := c.doublyLinkedList.Front().key
	c.doublyLinkedList.RemoveFromFront()
	return key
}

func (l *fifo) get(node *node, c *Cache) {
	fmt.Println("Shuffling doubly linked list due to get operation")
}

func (l *fifo) set(node *node, c *Cache) {
	fmt.Println("Shuffling doubly linked list due to set operation")
	c.doublyLinkedList.AddToEnd(node)
}

func (l *fifo) set_overwrite(node *node, value string, c *Cache) {
	fmt.Println("Shuffling doubly linked list due to set_overwrite operation")
}

cache.go

package main

import "fmt"

type Cache struct {
	doublyLinkedList *doublyLinkedList
	storage          map[string]*node
	evictionAlgo     evictionAlgo
	capacity         int
	maxCapacity      int
}

func initCache(evictionAlgo evictionAlgo, maxCapacity int) Cache {
	storage := make(map[string]*node)
	return Cache{
		doublyLinkedList: &doublyLinkedList{},
		storage:          storage,
		evictionAlgo:     evictionAlgo,
		capacity:         0,
		maxCapacity:      maxCapacity,
	}
}

func (this *Cache) setEvictionAlgo(e evictionAlgo) {
	this.evictionAlgo = e
}

func (this *Cache) set(key, value string) {
	node_ptr, ok := this.storage[key]
	if ok {
		this.evictionAlgo.set_overwrite(node_ptr, value, this)
		return
	}
	if this.capacity == this.maxCapacity {
		evictedKey := this.evict()
		delete(this.storage, evictedKey)
	}
	node := &node{key: key, value: value}
	this.storage[key] = node
	this.evictionAlgo.set(node, this)
	this.capacity++
}

func (this *Cache) get(key string) string {
	node_ptr, ok := this.storage[key]
	if ok {
		this.evictionAlgo.get(node_ptr, this)
		return (*node_ptr).value
	}
	return ""
}

func (this *Cache) evict() string {
	key := this.evictionAlgo.evict(this)
	this.capacity--
	return key
}

func (this *Cache) print() {
	for k, v := range this.storage {
		fmt.Printf("key :%s value: %s\n", k, (*v).value)
	}
	this.doublyLinkedList.TraverseForward()
}

Used in main.go

package main

import "fmt"

func main() {
	lru := createEvictioAlgo("lru")
	cache := initCache(lru, 3)
	cache.set("a", "1")
	cache.print()

	cache.set("b", "2")
	cache.print()

	cache.set("c", "3")
	cache.print()

	value := cache.get("a")
	fmt.Printf("key: a, value: %s\n", value)
	cache.print()

	cache.set("d", "4")
	cache.print()

	cache.set("e", "5")
	cache.print()
}
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