feat

size() func. added for linkedlist, doublylinkedlist stack and queue.

src/data-structures/doubly-linked-list/DoublyLinkedList.js

@@ -213,6 +213,10 @@ export default class DoublyLinkedList {
     return nodes;
   }
 
+  size() {
+    return this.toArray().length;
+  }
+
   /**
    * @param {*[]} values - Array of values that need to be converted to linked list.
    * @return {DoublyLinkedList}

src/data-structures/linked-list/LinkedList.js

@@ -233,6 +233,13 @@ export default class LinkedList {
 
     return nodes;
   }
+  
+  /**
+   * @return {number}
+   */
+  size() {
+    return this.toArray().length;
+  }
 
   /**
    * @param {function} [callback]

src/data-structures/queue/Queue.js

@@ -47,6 +47,14 @@ export default class Queue {
     return removedHead ? removedHead.value : null;
   }
 
+  /**
+   * @return {number}
+   */
+  size() {
+    return this.linkedList.size();
+  }
+
+  
   /**
    * @param [callback]
    * @return {string}

src/data-structures/stack/Stack.js

@@ -48,6 +48,13 @@ export default class Stack {
     return removedHead ? removedHead.value : null;
   }
 
+  /**
+   * @return {number}
+   */
+  size() {
+    return this.linkedList.size();
+  }
+
   /**
    * @return {*[]}
    */