clarify comments (#193)

src/data-structures/queue/Queue.js

@@ -2,10 +2,10 @@ import LinkedList from '../linked-list/LinkedList';
 
 export default class Queue {
   constructor() {
-    // We're going to implement Queue based on LinkedList since this
-    // structures a quite similar. Namely they both operates mostly with
-    // with theirs beginning and the end. Compare enqueue/de-queue
-    // operations of the Queue with append/prepend operations of LinkedList.
+    // We're going to implement Queue based on LinkedList since the two
+    // structures are quite similar. Namely, they both operate mostly on
+    // the elements at the beginning and the end. Compare enqueue/dequeue
+    // operations of Queue with append/deleteHead operations of LinkedList.
     this.linkedList = new LinkedList();
   }
 
@@ -13,39 +13,36 @@ export default class Queue {
    * @return {boolean}
    */
   isEmpty() {
-    // The queue is empty in case if its linked list don't have tail.
-    return !this.linkedList.tail;
+    return !this.linkedList.head;
   }
 
   /**
+   * Read the element at the front of the queue without removing it.
    * @return {*}
    */
   peek() {
     if (!this.linkedList.head) {
-      // If linked list is empty then there is nothing to peek from.
       return null;
     }
 
-    // Just read the value from the end of linked list without deleting it.
     return this.linkedList.head.value;
   }
 
   /**
+   * Add a new element to the end of the queue (the tail of the linked list).
+   * This element will be processed after all elements ahead of it.
    * @param {*} value
    */
   enqueue(value) {
-    // Enqueueing means to stand in the line. Therefore let's just add
-    // new value at the beginning of the linked list. It will need to wait
-    // until all previous nodes will be processed.
     this.linkedList.append(value);
   }
 
   /**
+   * Remove the element at the front of the queue (the head of the linked list).
+   * If the queue is empty, return null.
    * @return {*}
    */
   dequeue() {
-    // Let's try to delete the last node from linked list (the tail).
-    // If there is no tail in linked list (it is empty) just return null.
     const removedHead = this.linkedList.deleteHead();
     return removedHead ? removedHead.value : null;
   }