11import PriorityQueue from '../../../data-structures/priority-queue/PriorityQueue' ;
22
33/**
4- * @param {Graph } graph
5- * @param {GraphVertex } startVertex
4+ * @typedef {Object } ShortestPaths
5+ * @property {Object } distances - shortest distances to all vertices
6+ * @property {Object } previousVertices - shortest paths to all vertices.
7+ */
8+ 9+ /**
10+ * Implementation of Dijkstra algorithm of finding the shortest paths to graph nodes.
11+ * @param {Graph } graph - graph we're going to traverse.
12+ * @param {GraphVertex } startVertex - traversal start vertex.
13+ * @return {ShortestPaths }
614 */
715export default function dijkstra ( graph , startVertex ) {
16+ // Init helper variables that we will need for Dijkstra algorithm.
817 const distances = { } ;
918 const visitedVertices = { } ;
1019 const previousVertices = { } ;
1120 const queue = new PriorityQueue ( ) ;
1221
1322 // Init all distances with infinity assuming that currently we can't reach
14- // any of the vertices except start one.
23+ // any of the vertices except the start one.
1524 graph . getAllVertices ( ) . forEach ( ( vertex ) => {
1625 distances [ vertex . getKey ( ) ] = Infinity ;
1726 previousVertices [ vertex . getKey ( ) ] = null ;
1827 } ) ;
28+ 29+ // We are already at the startVertex so the distance to it is zero.
1930 distances [ startVertex . getKey ( ) ] = 0 ;
2031
2132 // Init vertices queue.
2233 queue . add ( startVertex , distances [ startVertex . getKey ( ) ] ) ;
2334
35+ // Iterate over the priority queue of vertices until it is empty.
2436 while ( ! queue . isEmpty ( ) ) {
37+ // Fetch next closest vertex.
2538 const currentVertex = queue . poll ( ) ;
2639
27- graph . getNeighbors ( currentVertex ) . forEach ( ( neighbor ) => {
40+ // Iterate over every unvisited neighbor of the current vertex.
41+ currentVertex . getNeighbors ( ) . forEach ( ( neighbor ) => {
2842 // Don't visit already visited vertices.
2943 if ( ! visitedVertices [ neighbor . getKey ( ) ] ) {
3044 // Update distances to every neighbor from current vertex.
@@ -33,15 +47,16 @@ export default function dijkstra(graph, startVertex) {
3347 const existingDistanceToNeighbor = distances [ neighbor . getKey ( ) ] ;
3448 const distanceToNeighborFromCurrent = distances [ currentVertex . getKey ( ) ] + edge . weight ;
3549
50+ // If we've found shorter path to the neighbor - update it.
3651 if ( distanceToNeighborFromCurrent < existingDistanceToNeighbor ) {
3752 distances [ neighbor . getKey ( ) ] = distanceToNeighborFromCurrent ;
3853
39- // Change priority.
54+ // Change priority of the neighbor in a queue since it might have became closer .
4055 if ( queue . hasValue ( neighbor ) ) {
4156 queue . changePriority ( neighbor , distances [ neighbor . getKey ( ) ] ) ;
4257 }
4358
44- // Remember previous vertex.
59+ // Remember previous closest vertex.
4560 previousVertices [ neighbor . getKey ( ) ] = currentVertex ;
4661 }
4762
@@ -52,10 +67,12 @@ export default function dijkstra(graph, startVertex) {
5267 }
5368 } ) ;
5469
55- // Add current vertex to visited ones.
70+ // Add current vertex to visited ones to avoid visiting it again later .
5671 visitedVertices [ currentVertex . getKey ( ) ] = currentVertex ;
5772 }
5873
74+ // Return the set of shortest distances to all vertices and the set of
75+ // shortest paths to all vertices in a graph.
5976 return {
6077 distances,
6178 previousVertices,
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