Create LRU Cache.js

Author: paopao2

LRU Cache.js

@@ -0,0 +1,103 @@
+/**
+Design and implement a data structure for Least Recently Used (LRU) cache. It should support the following operations: get and set.
+
+get(key) - Get the value (will always be positive) of the key if the key exists in the cache, otherwise return -1.
+set(key, value) - Set or insert the value if the key is not already present. When the cache reached its capacity, it should invalidate the least recently used item before inserting a new item.
+*/
+class Node {
+    constructor(key, val) {
+        this.key = key;
+        this.val = val;
+        this.next = null;
+        this.prev = null;
+    }
+}
+/**
+ * @constructor
+ */
+var LRUCache = function(capacity) {
+    this.list = null;
+    this.map = new Map();
+    this.head = null;
+    this.tail = null;
+    this.size = capacity;
+    this.curSize = 0;
+};
+
+/**
+ * @param {number} key
+ * @returns {number}
+ */
+LRUCache.prototype.get = function(key) {
+    if (!this.map.get(key)) {
+        return -1;
+    }
+    
+    let node = this.map.get(key);
+    
+    if (node === this.head) {
+        return node.val;
+    }
+    
+    // remove node from list
+    if (node === this.tail) {
+        this.tail.prev.next = null;
+        this.tail = this.tail.prev;
+    } else {
+        node.prev.next = node.next;
+        node.next.prev = node.prev;
+    }
+    
+    // insert node to head
+    node.next = this.head;
+    this.head.prev = node;
+    this.head = node;
+    
+    return node.val;
+};
+
+/**
+ * @param {number} key
+ * @param {number} value
+ * @returns {void}
+ */
+LRUCache.prototype.set = function(key, value) {
+    let newNode = new Node(key, value);
+    
+    if (this.curSize === 0) {
+        this.head = newNode;
+        this.tail = newNode;
+        this.curSize++;
+    } else {
+        newNode.next = this.head;
+        this.head.prev = newNode;
+        this.head = newNode;
+        this.curSize++;
+    }
+    
+    // update
+    if (this.map.get(key)) {
+        let oldNode = this.map.get(key);
+        
+        if (oldNode === this.tail) {
+            this.tail = this.tail.prev;
+            this.tail.next = null;
+        } else {
+            oldNode.prev.next = oldNode.next;
+            oldNode.next.prev = oldNode.prev;
+        }
+        
+        this.curSize--;
+        this.map.set(key, newNode);
+    } else {
+        if (this.curSize > this.size) {
+            //delete tail
+            this.map.delete(this.tail.key);
+            this.tail = this.tail.prev;
+            this.tail.next = null;
+            this.curSize--;
+        }
+        
+        this.map.set(key, newNode);
+    }
+};