11import MinHeap from '../heap/MinHeap' ;
22import Comparator from '../../utils/comparator/Comparator' ;
33
4- // It is the same as min heap except that when comparing to elements
5- // we take into account not element's value but rather its priority .
4+ // It is the same as min heap except that when comparing two elements
5+ // we take into account its priority instead of the element's value .
66export default class PriorityQueue extends MinHeap {
77 constructor ( ) {
8+ // Call MinHip constructor first.
89 super ( ) ;
9- this . priorities = { } ;
10+ 11+ // Setup priorities map.
12+ this . priorities = new Map ( ) ;
13+ 14+ // Use custom comparator for heap elements that will take element priority
15+ // instead of element value into account.
1016 this . compare = new Comparator ( this . comparePriority . bind ( this ) ) ;
1117 }
1218
1319 /**
14- * @param {* } item
15- * @param {number } [priority]
20+ * Add item to the priority queue.
21+ * @param {* } item - item we're going to add to the queue.
22+ * @param {number } [priority] - items priority.
1623 * @return {PriorityQueue }
1724 */
1825 add ( item , priority = 0 ) {
19- this . priorities [ item ] = priority ;
26+ this . priorities . set ( item , priority ) ;
2027 super . add ( item ) ;
21- 2228 return this ;
2329 }
2430
2531 /**
26- * @param {* } item
27- * @param {Comparator } [customFindingComparator]
32+ * Remove item from priority queue.
33+ * @param {* } item - item we're going to remove.
34+ * @param {Comparator } [customFindingComparator] - custom function for finding the item to remove
2835 * @return {PriorityQueue }
2936 */
3037 remove ( item , customFindingComparator ) {
3138 super . remove ( item , customFindingComparator ) ;
32- delete this . priorities [ item ] ;
33- 39+ this . priorities . delete ( item ) ;
3440 return this ;
3541 }
3642
3743 /**
38- * @param {* } item
39- * @param {number } priority
44+ * Change priority of the item in a queue.
45+ * @param {* } item - item we're going to re-prioritize.
46+ * @param {number } priority - new item's priority.
4047 * @return {PriorityQueue }
4148 */
4249 changePriority ( item , priority ) {
4350 this . remove ( item , new Comparator ( this . compareValue ) ) ;
4451 this . add ( item , priority ) ;
45- 4652 return this ;
4753 }
4854
4955 /**
56+ * Find item by ite value.
5057 * @param {* } item
5158 * @return {Number[] }
5259 */
@@ -55,6 +62,7 @@ export default class PriorityQueue extends MinHeap {
5562 }
5663
5764 /**
65+ * Check if item already exists in a queue.
5866 * @param {* } item
5967 * @return {boolean }
6068 */
@@ -63,19 +71,20 @@ export default class PriorityQueue extends MinHeap {
6371 }
6472
6573 /**
74+ * Compares priorities of two items.
6675 * @param {* } a
6776 * @param {* } b
6877 * @return {number }
6978 */
7079 comparePriority ( a , b ) {
71- if ( this . priorities [ a ] === this . priorities [ b ] ) {
80+ if ( this . priorities . get ( a ) === this . priorities . get ( b ) ) {
7281 return 0 ;
7382 }
74- 75- return this . priorities [ a ] < this . priorities [ b ] ? - 1 : 1 ;
83+ return this . priorities . get ( a ) < this . priorities . get ( b ) ? - 1 : 1 ;
7684 }
7785
7886 /**
87+ * Compares values of two items.
7988 * @param {* } a
8089 * @param {* } b
8190 * @return {number }
@@ -84,7 +93,6 @@ export default class PriorityQueue extends MinHeap {
8493 if ( a === b ) {
8594 return 0 ;
8695 }
87- 8896 return a < b ? - 1 : 1 ;
8997 }
9098}
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