simplify public interface of the solver

Author: j50n

README.md

@@ -2,7 +2,11 @@
 
 A pretty good implementation of Dijkstra's shortest-path algorithm.
 
-This implementation is designed to process large in-memory graphs. It will perform reasonably well even when the number of edges is in the millions. Using numbered indexes for nodes, rather than string labels or objects, was by design. This reduced the memory footprint needed for the graph and speeds up graph creation and lookups. 
+This implementation is designed to process large in-memory graphs. It will
+perform reasonably well even when the number of edges is in the millions. Using
+numbered indexes for nodes, rather than string labels or objects, was by design.
+This reduced the memory footprint needed for the graph and speeds up graph
+creation and lookups.
 
 This code was adapted to Typescript/Deno from
 [A Walkthrough of Dijkstra's Algorithm (In JavaScript!)](https://medium.com/@adriennetjohnson/a-walkthrough-of-dijkstras-algorithm-in-javascript-e94b74192026)

dijkstra.ts

@@ -29,8 +29,7 @@ interface IPath {
  */
 export class DijkstraShortestPathSolver {
   private constructor(
-    public readonly nodes: number,
-    public readonly adjacencyList: IEdge[][],
+    protected readonly adjacencyList: IEdge[][],
   ) {
   }
 
@@ -41,7 +40,6 @@ export class DijkstraShortestPathSolver {
    */
   static init(nodes: number): DijkstraShortestPathSolver {
     return new DijkstraShortestPathSolver(
-      nodes,
       new Array(nodes).fill(null).map((_v) => new Array(0)),
     );
   }
@@ -52,11 +50,17 @@ export class DijkstraShortestPathSolver {
    */
   clone(): DijkstraShortestPathSolver {
     return new DijkstraShortestPathSolver(
-      this.nodes,
       this.adjacencyList.map((a) => a.slice(0)),
     );
   }
 
+  /**
+   * The number of nodes in the graph.
+   */
+  protected get nodes(): number {
+    return this.adjacencyList.length;
+  }
+
   /**
    * Add an edge (in one direction).
    * @param fromNode Starting node.