implement queue using a linked list

Author: amejiarosario

lib/data-structures/queues/queue-1.js

@@ -1,15 +1,35 @@
+/**
+ * Data structure where add and remove elements in a first-in, first-out (FIFO)
+ */
 class Queue {
   constructor() {
     this.input = [];
   }
 
+  /**
+   * Add element to the queue
+   * Runtime: O(1)
+   * @param {any} element
+   */
   add(element) {
     this.input.push(element);
   }
 
+  /**
+   * Add element to the queue
+   * Runtime: O(1)
+   * @param {any} element
+   */
   remove() {
     return this.input.shift();
   }
+
+  /**
+   * Size of the queue
+   */
+  get size() {
+    return this.input.length;
+  }
 }
 
 module.exports = Queue;

lib/data-structures/queues/queue-2.js

@@ -0,0 +1,45 @@
+/**
+ * Data structure where add and remove elements in a first-in, first-out (FIFO)
+ */
+class Queue {
+  constructor() {
+    this.input = [];
+    this.output = [];
+  }
+
+  /**
+   * Add element to the queue
+   * Runtime: O(1)
+   * @param {any} element
+   */
+  add(element) {
+    this.input.push(element);
+  }
+
+  /**
+   * Remove element from the queue
+   * Runtime: O(n)
+   * Amortized runtime: O(1)*
+   */
+  remove() {
+    if(!this.output.length) {
+      while(this.input.length) {
+        this.output.push(this.input.pop());
+      }
+    }
+    return this.output.pop();
+  }
+
+  /**
+   * Size of the queue
+   */
+  get size() {
+    return this.input.length + this.output.length;
+  }
+}
+
+// Aliases
+Queue.prototype.enqueue = Queue.prototype.add;
+Queue.prototype.dequeue = Queue.prototype.remove;
+
+module.exports = Queue;

lib/data-structures/queues/queue.js

@@ -1,21 +1,40 @@
+const LinkedList = require('../linked-lists/linked-list');
+
+/**
+ * Data structure where add and remove elements in a first-in, first-out (FIFO)
+ */
 class Queue {
   constructor() {
-    this.input = [];
-    this.output = [];
+    this.input = new LinkedList();
   }
 
+  /**
+   * Add element to the queue
+   * Runtime: O(1)
+   * @param {any} element
+   */
   add(element) {
-    this.input.push(element);
+    this.input.addFirst(element);
   }
 
+  /**
+   * Remove element from the queue
+   * Runtime: O(1)
+   */
   remove() {
-    if(!this.output.length) {
-      while(this.input.length) {
-        this.output.push(this.input.pop());
-      }
-    }
-    return this.output.pop();
+    return this.input.removeLast();
+  }
+
+  /**
+   * Size of the queue
+   */
+  get size() {
+    return this.input.size;
   }
 }
 
+// Aliases
+Queue.prototype.enqueue = Queue.prototype.add;
+Queue.prototype.dequeue = Queue.prototype.remove;
+
 module.exports = Queue;

lib/data-structures/queues/queue.spec.js

@@ -1,4 +1,4 @@
-const Queue = require('./queue.js');
+const Queue = require('./queue-2.js');
 
 describe('Queue', function () {
   let queue;
@@ -9,8 +9,9 @@ describe('Queue', function () {
 
   describe('#add', () => {
     it('should push an element to the queue', () => {
+      expect(queue.size).toEqual(0);
       queue.add(1);
-      expect(queue.input).toEqual([1]);
+      expect(queue.size).toEqual(1);
     });
   });