Add Dijkstra's algorithm to Typescript (#291)

09_dijkstras_algorithm/ts/dijkstras_algorithm.ts

@@ -0,0 +1,59 @@
+import { Graph, GraphIterable } from "./iterable_graph";
+
+const dijkstraGraph: Graph<Graph<number>> = {
+  start: { a: 6, b: 2 },
+  a: { fin: 1 },
+  b: { a: 3, fin: 5 },
+  fin: {},
+};
+
+const costs: Graph<number> = {
+  a: 6,
+  b: 2,
+  fin: Infinity,
+};
+
+const parents: Graph<string | null> = {
+  a: "start",
+  b: "start",
+  fin: null,
+};
+
+let processed: string[] = [];
+
+const findLowestCostNode = (costs: Graph<number>): string | null => {
+  let lowestCost = Infinity;
+  let lowestCostNode: string | null = null;
+
+  const iterableGraph = new GraphIterable(costs);
+
+  for (const node of iterableGraph) {
+    const cost = costs[node];
+    if (cost < lowestCost && !processed.includes(node)) {
+      lowestCost = cost;
+      lowestCostNode = node;
+    }
+  }
+  return lowestCostNode;
+};
+
+let node = findLowestCostNode(costs);
+
+while (node !== null) {
+  const cost = costs[node];
+
+  const neighbors = dijkstraGraph[node];
+  Object.keys(neighbors).forEach((n: string) => {
+    const newCost = cost + neighbors[n];
+    if (costs[n] > newCost) {
+      costs[n] = newCost;
+      parents[n] = node;
+    }
+  });
+
+  processed.push(node);
+  node = findLowestCostNode(costs);
+}
+
+console.log("Cost from the start to each node:");
+console.log(costs); // { a: 5, b: 2, fin: 6 }

09_dijkstras_algorithm/ts/iterable_graph.ts

@@ -0,0 +1,26 @@
+export interface Graph<T> {
+  [key: string]: T;
+}
+
+export class GraphIterable<T> implements Iterable<string> {
+  private graph: Graph<T>;
+
+  constructor(graph: Graph<T>) {
+    this.graph = graph;
+  }
+
+  [Symbol.iterator](): Iterator<string> {
+    const keys = Object.keys(this.graph);
+    let index = 0;
+
+    return {
+      next: (): IteratorResult<string> => {
+        if (index < keys.length) {
+          return { value: keys[index++], done: false };
+        } else {
+          return { value: undefined, done: true };
+        }
+      },
+    };
+  }
+}