Add Dijkstra.

Author: Cheap Interest Rates On Credit Cards

src/algorithms/graph/dijkstra/__test__/dijkstra.test.js

@@ -43,7 +43,7 @@ describe('dijkstra', () => {
  .addEdge(edgeFG)
  .addEdge(edgeEG);
 
- const distances = dijkstra(graph, vertexA);
+ const { distances, previousVertices } = dijkstra(graph, vertexA);
 
  expect(distances).toEqual({
  H: Infinity,
@@ -55,5 +55,11 @@ describe('dijkstra', () => {
  G: 12,
  F: 11,
  });
+
+ expect(previousVertices.F.getKey()).toBe('D');
+ expect(previousVertices.D.getKey()).toBe('B');
+ expect(previousVertices.B.getKey()).toBe('A');
+ expect(previousVertices.G.getKey()).toBe('E');
+ expect(previousVertices.C.getKey()).toBe('A');
  });
 });

src/algorithms/graph/dijkstra/dijkstra.js

@@ -7,6 +7,7 @@ import PriorityQueue from '../../../data-structures/priority-queue/PriorityQueue
 export default function dijkstra(graph, startVertex) {
  const distances = {};
  const visitedVertices = {};
+ const previousVertices = {};
  const queue = new PriorityQueue();
 
  // Init all distances with infinity assuming that currently we can't reach
@@ -38,6 +39,9 @@ export default function dijkstra(graph, startVertex) {
  if (queue.hasValue(neighbor)) {
  queue.changePriority(neighbor, distances[neighbor.getKey()]);
  }
+
+ // Remember previous vertex.
+ previousVertices[neighbor.getKey()] = currentVertex;
  }
 
  // Add neighbor to the queue for further visiting.
@@ -51,5 +55,8 @@ export default function dijkstra(graph, startVertex) {
  visitedVertices[currentVertex.getKey()] = currentVertex;
  }
 
- return distances;
+ return {
+ distances,
+ previousVertices,
+ };
 }