dist-javascript-algorithms-and-data-structures/dist/algorithms/graph/bellman-ford/bellmanFord.js

Algorithms and data-structures implemented on JavaScript

"use strict";

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

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

  distances[startVertex.getKey()] = 0;
  graph.getAllVertices().forEach(vertex => {
    previousVertices[vertex.getKey()] = null;

    if (vertex.getKey() !== startVertex.getKey()) {
      distances[vertex.getKey()] = Infinity;
    }
  }); // We need (|V| - 1) iterations.

  for (let iteration = 0; iteration < graph.getAllVertices().length - 1; iteration += 1) {
    // During each iteration go through all vertices.
    Object.keys(distances).forEach(vertexKey => {
      const vertex = graph.getVertexByKey(vertexKey); // Go through all vertex edges.

      graph.getNeighbors(vertex).forEach(neighbor => {
        const edge = graph.findEdge(vertex, neighbor); // Find out if the distance to the neighbor is shorter in this iteration
        // then in previous one.

        const distanceToVertex = distances[vertex.getKey()];
        const distanceToNeighbor = distanceToVertex + edge.weight;

        if (distanceToNeighbor < distances[neighbor.getKey()]) {
          distances[neighbor.getKey()] = distanceToNeighbor;
          previousVertices[neighbor.getKey()] = vertex;
        }
      });
    });
  }

  return {
    distances,
    previousVertices
  };
}