fix(pathfinding): use real cost in A* instead of greedy heuristic

updateNeighborNode overwrote gScore with the heuristic, so A* behaved like greedy best-first search and found longer paths than Dijkstra.

src/app/pages/algorithms/pathfinding/service/pathfinding.service.spec.ts

@@ -117,6 +117,30 @@ describe('PathfindingService', () => {
       expect(nodesInShortestPathOrder[0]).toBe(start);
       expect(nodesInShortestPathOrder[nodesInShortestPathOrder.length - 1]).toBe(end);
     });
+
+    it('finds a path as short as Dijkstra on random grids', () => {
+      let seed = 12345;
+      const random = (): number => (seed = (seed * 1664525 + 1013904223) % 4294967296) / 4294967296;
+      for (let run = 0; run < 20; run++) {
+        const build = (): Node[][] => {
+          seed = 1000 + run;
+          const grid = createGrid(20, 20);
+          for (const node of grid.flat()) {
+            node.isWall = random() < 0.3;
+          }
+          grid[0][0].isWall = false;
+          grid[19][19].isWall = false;
+          return grid;
+        };
+        const astarGrid = build();
+        const dijkstraGrid = build();
+
+        const astar = service.aStar(astarGrid, astarGrid[0][0], astarGrid[19][19]);
+        const dijkstra = service.dijkstra(dijkstraGrid, dijkstraGrid[0][0], dijkstraGrid[19][19]);
+
+        expect(astar.nodesInShortestPathOrder.length).toBe(dijkstra.nodesInShortestPathOrder.length);
+      }
+    });
   });
 
   describe('findPath', () => {

src/app/pages/algorithms/pathfinding/service/pathfinding.service.ts

@@ -155,7 +155,6 @@ export class PathfindingService {
   private updateNeighborNode(neighbor: Node, currentNode: Node, tentativeGScore: number, endNode: Node, openSet: Node[]) {
     neighbor.linkedNode = currentNode;
     neighbor.nodeData = tentativeGScore;
-    neighbor['nodeData'] = this.calculateHeuristic(neighbor, endNode);
     neighbor['hScore'] = this.calculateHeuristic(neighbor, endNode);
     neighbor['fScore'] = neighbor.nodeData + neighbor['hScore'];