artello73 / dijkstra-ts

Implementation of Dijkstra's algorithm in TypeScript

Dijkstra TypeScript

A simple implementation of Dijkstra's algorithm using the Priority queue implementation priorityqueue.js. Using a Priority queue we can achieve a runtime complexity of O(E*log V) where E is the total number of edges and V is the number vertices(called nodes in this package). More about the runtime complexity can be found on Wikipedia.

Installation

npm install https://github.com/kaisnb/dijkstra-ts.git

Example

The implementation makes no assumption about the datastructure you use to store your graph. To use the algorithm we just need to create an adapter that implements the IGraphAdapter<T> interface. To implement this interface we just need to implement the method getEdges(n: T): Edge<T>[]. T can be an object type or a primitive type. In case it's an object type we also have to implement the getKey(n: T): NodeKey method to map our nodes to unique keys.

import { Edge, findShortestPath, IGraphAdapter } from "dijkstra-ts";

export type GraphType = Record<string, Record<string, number>>;

export class GraphAdapter implements IGraphAdapter<string> {
  graph: GraphType;

  constructor(graph: GraphType) {
    this.graph = graph;
  }

  getEdges(n: string): Edge<string>[] {
    return Object.entries(this.graph[n]).map(([key, value]) => ({
      node: key,
      weight: value,
    }));
  }
}

export const startNode = "start";
export const finishNode = "finish";
export const graph: GraphType = {
  [startNode]: { A: 5, B: 2 },
  A: { C: 4, D: 2 },
  B: { A: 8, D: 7 },
  C: { D: 6, [finishNode]: 3 },
  D: { [finishNode]: 1 },
  [finishNode]: {},
};

const result = findShortestPath(new GraphAdapter(graph), startNode, finishNode);

console.log(result); // { distance: 8, path: [ 'start', 'A', 'D', 'finish' ] }

Or to obtain a map of the costs of all paths and all the calculated parent nodes, call dijkstra<T>(adapter: IGraphAdapter<T>, startNode: T, finishNode?: T) instead. It's optional to pass the finishNode. In case the finishNode is passed (like it's done indirectly when called via findShortestPath) the resulting cost and parent maps can be uncomplete because an optimization takes place and the algorithm returns as early as the shortest path to the finishNode is found.

For more usage examples see the test test/dijkstra.test.ts and the example adapters under test/graphs.

License

Everything in this repository is licensed under the MIT License unless otherwise specified.

Copyright (c) 2021 Kai Schönberger