// https://medium.com/dsinjs/implementing-lru-cache-in-javascript-94ba6755cda9
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class Node {
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constructor(key, value, next = null, prev = null) {
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this.key = key;
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this.value = value;
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this.next = next;
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this.prev = prev;
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}
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}
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export default class LRUCache {
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//set default limit of 10 if limit is not passed.
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constructor(limit = 10) {
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this.size = 0;
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this.limit = limit;
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this.head = null;
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this.tail = null;
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this.cache = {};
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}
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// Write Node to head of LinkedList
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// update cache with Node key and Node reference
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put(key, value){
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this.ensureLimit();
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if(!this.head){
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this.head = this.tail = new Node(key, value);
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}else{
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const node = new Node(key, value, this.head);
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this.head.prev = node;
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this.head = node;
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}
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//Update the cache map
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this.cache[key] = this.head;
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this.size++;
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}
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// Read from cache map and make that node as new Head of LinkedList
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get(key){
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if(this.cache[key]){
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const value = this.cache[key].value;
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// node removed from it's position and cache
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this.remove(key)
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// write node again to the head of LinkedList to make it most recently used
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this.put(key, value);
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return value;
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}
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console.log(`Item not available in cache for key ${key}`);
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}
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ensureLimit(){
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if(this.size === this.limit){
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this.remove(this.tail.key)
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}
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}
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remove(key){
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const node = this.cache[key];
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if(node.prev !== null){
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node.prev.next = node.next;
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}else{
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this.head = node.next;
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}
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if(node.next !== null){
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node.next.prev = node.prev;
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}else{
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this.tail = node.prev
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}
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delete this.cache[key];
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this.size--;
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}
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clear() {
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this.head = null;
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this.tail = null;
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this.size = 0;
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this.cache = {};
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}
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// // Invokes the callback function with every node of the chain and the index of the node.
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// forEach(fn) {
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// let node = this.head;
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// let counter = 0;
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// while (node) {
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// fn(node, counter);
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// node = node.next;
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// counter++;
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// }
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// }
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// // To iterate over LRU with a 'for...of' loop
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// *[Symbol.iterator]() {
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// let node = this.head;
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// while (node) {
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// yield node;
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// node = node.next;
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// }
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// }
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}
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