dist-javascript-algorithms-and-data-structures/dist/algorithms/graph/dijkstra/dijkstra.js

Algorithms and data-structures implemented on JavaScript

"use strict";

Object.defineProperty(exports, "__esModule", {
  value: true
});
exports.default = dijkstra;

var _PriorityQueue = _interopRequireDefault(require("../../../data-structures/priority-queue/PriorityQueue"));

function _interopRequireDefault(obj) { return obj && obj.__esModule ? obj : { default: obj }; }

/**
 * @param {Graph} graph
 * @param {GraphVertex} startVertex
 */
function dijkstra(graph, startVertex) {
  const distances = {};
  const visitedVertices = {};
  const previousVertices = {};
  const queue = new _PriorityQueue.default(); // Init all distances with infinity assuming that currently we can't reach
  // any of the vertices except start one.

  graph.getAllVertices().forEach(vertex => {
    distances[vertex.getKey()] = Infinity;
    previousVertices[vertex.getKey()] = null;
  });
  distances[startVertex.getKey()] = 0; // Init vertices queue.

  queue.add(startVertex, distances[startVertex.getKey()]);

  while (!queue.isEmpty()) {
    const currentVertex = queue.poll();
    graph.getNeighbors(currentVertex).forEach(neighbor => {
      // Don't visit already visited vertices.
      if (!visitedVertices[neighbor.getKey()]) {
        // Update distances to every neighbor from current vertex.
        const edge = graph.findEdge(currentVertex, neighbor);
        const existingDistanceToNeighbor = distances[neighbor.getKey()];
        const distanceToNeighborFromCurrent = distances[currentVertex.getKey()] + edge.weight;

        if (distanceToNeighborFromCurrent < existingDistanceToNeighbor) {
          distances[neighbor.getKey()] = distanceToNeighborFromCurrent; // Change priority.

          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.


        if (!queue.hasValue(neighbor)) {
          queue.add(neighbor, distances[neighbor.getKey()]);
        }
      }
    }); // Add current vertex to visited ones.

    visitedVertices[currentVertex.getKey()] = currentVertex;
  }

  return {
    distances,
    previousVertices
  };
}