@@ -2,13 +2,17 @@ import LinkedList from '../linked-list/LinkedList';
22
33export default class Stack {
44constructor ( ) {
5+ // We're going to implement Queue based on LinkedList since this
6+ // structures a quite similar. Compare push/pop operations of the Stack
7+ // with append/deleteTail operations of LinkedList.
58this . linkedList = new LinkedList ( ) ;
69}
710
811/**
912 *@return {boolean }
1013 */
1114isEmpty ( ) {
15+ // The queue is empty in case if its linked list don't have tail.
1216return ! this . linkedList . tail ;
1317}
1418
@@ -17,23 +21,29 @@ export default class Stack {
1721 */
1822peek ( ) {
1923if ( this . isEmpty ( ) ) {
24+ // If linked list is empty then there is nothing to peek from.
2025return null ;
2126}
2227
28+ // Just read the value from the end of linked list without deleting it.
2329return this . linkedList . tail . value ;
2430}
2531
2632/**
2733 *@param {* } value
2834 */
2935push ( value ) {
36+ // Pushing means to lay the value on top of the stack. Therefore let's just add
37+ // new value at the end of the linked list.
3038this . linkedList . append ( value ) ;
3139}
3240
3341/**
3442 *@return {* }
3543 */
3644pop ( ) {
45+ // Let's try to delete the last node from linked list (the tail).
46+ // If there is no tail in linked list (it is empty) just return null.
3747const removedTail = this . linkedList . deleteTail ( ) ;
3848return removedTail ?removedTail . value :null ;
3949}