merge: fix TheAlgorithms#844 (TheAlgorithms#846)

* fix TheAlgorithms#844

* formatted code according to standard.js

Author: aditya1944

Cache/LRUCache.js

@@ -1,88 +1,39 @@
-class DoubleLinkedListNode {
-  // Double Linked List Node built specifically for LRU Cache
-  constructor (key, val) {
-    this.key = key
-    this.val = val
-    this.next = null
-    this.prev = null
-  }
-}
-
-class DoubleLinkedList {
-  // Double Linked List built specifically for LRU Cache
-  constructor () {
-    this.head = new DoubleLinkedListNode(null, null)
-    this.rear = new DoubleLinkedListNode(null, null)
-    this.head.next = this.rear
-    this.rear.prev = this.head
-  }
-
-  add (node) {
-    // Adds the given node to the end of the list (before rear)
-    const temp = this.rear.prev
-    temp.next = node
-    node.prev = temp
-    this.rear.prev = node
-    node.next = this.rear
-  }
-
-  remove (node) {
-    // Removes and returns the given node from the list
-    const tempLast = node.prev
-    const tempNext = node.next
-    node.prev = null
-    node.next = null
-    tempLast.next = tempNext
-    tempNext.prev = tempLast
-
-    return node
-  }
-}
-
 class LRUCache {
   // LRU Cache to store a given capacity of data
   constructor (capacity) {
-    this.list = new DoubleLinkedList()
+    this.cache = new Map()
     this.capacity = capacity
-    this.numKeys = 0
     this.hits = 0
     this.miss = 0
-    this.cache = {}
   }
 
   cacheInfo () {
     // Return the details for the cache instance [hits, misses, capacity, current_size]
-    return `CacheInfo(hits=${this.hits}, misses=${this.miss}, capacity=${this.capacity}, current size=${this.numKeys})`
+    return `CacheInfo(hits=${this.hits}, misses=${this.miss}, capacity=${this.capacity}, current size=${this.cache.size})`
   }
 
   set (key, value) {
-    // Sets the value for the input key and updates the Double Linked List
-    if (!(key in this.cache)) {
-      if (this.numKeys >= this.capacity) {
-        const keyToDelete = this.list.head.next.key
-        this.list.remove(this.cache[keyToDelete])
-        delete this.cache[keyToDelete]
-        this.numKeys -= 1
-      }
-      this.cache[key] = new DoubleLinkedListNode(key, value)
-      this.list.add(this.cache[key])
-      this.numKeys += 1
-    } else {
-      const node = this.list.remove(this.cache[key])
-      node.val = value
-      this.list.add(node)
+    // Sets the value for the input key and if the key exists it updates the existing key
+    if (this.cache.size === this.capacity) {
+      // delete oldest key existing in map
+      this.cache.delete(this.cache.keys().next().value)
     }
+    this.cache.set(key, value)
   }
 
   get (key) {
-    // Returns the value for the input key and updates the Double Linked List. Returns null if key is not present in cache
-    if (key in this.cache) {
+    // Returns the value for the input key. Returns null if key is not present in cache
+    if (this.cache.has(key)) {
+      const value = this.cache.get(key)
+      // refresh the cache to update the order of key
+      this.cache.delete(key)
+      this.cache.set(key, value)
       this.hits += 1
-      this.list.add(this.list.remove(this.cache[key]))
-      return this.cache[key].val
+      return value
+    } else {
+      this.miss += 1
+      return null
     }
-    this.miss += 1
-    return null
   }
 }