refactor: deduplicate DijkstraEntry between GraphUtils and ShortestPathFinder

ShortestPathFinder had its own private DijkstraEntry class that was
identical to the one in GraphUtils. Made GraphUtils.DijkstraEntry
package-visible and updated ShortestPathFinder to reuse it.

This eliminates a duplicated inner class (~15 lines) and ensures any
future improvements to the PQ entry type only need to happen in one
place.

Author: sauravbhattacharya001

Gvisual/src/gvisual/GraphUtils.java

@@ -626,10 +626,10 @@ public static DijkstraResult dijkstra(Graph<String, Edge> graph, String source)
      * int-to-vertex lookups. Eliminates O(V) index bookkeeping and
      * fragile double-to-int casting on every PQ poll.
      *
-     * <p>Consistent with the approach already used in
-     * {@link ShortestPathFinder}.</p>
+     * <p>Package-visible so that {@link ShortestPathFinder} can reuse
+     * the same entry type instead of maintaining its own duplicate.</p>
      */
-    private static final class DijkstraEntry implements Comparable<DijkstraEntry> {
+    static final class DijkstraEntry implements Comparable<DijkstraEntry> {
         final double distance;
         final String vertex;
 

Gvisual/src/gvisual/ShortestPathFinder.java

@@ -141,7 +141,7 @@ public PathResult findShortestByHops(String source, String target) {
     /**
      * Finds the shortest path by total Edge weight (Dijkstra) between source and target.
      *
-     * <p>Uses a typed {@link DijkstraEntry} in the priority queue for clean
+     * <p>Uses a typed {@link GraphUtils.DijkstraEntry} in the priority queue for clean
      * vertex lookups without index indirection or double-to-int casting.</p>
      *
      * @param source source vertex ID
@@ -168,16 +168,16 @@ public PathResult findShortestByWeight(String source, String target) {
         Map<String, String> predecessor = new HashMap<String, String>();
         Map<String, Edge> predecessorEdge = new HashMap<String, Edge>();
 
-        PriorityQueue<DijkstraEntry> pq = new PriorityQueue<DijkstraEntry>();
+        PriorityQueue<GraphUtils.DijkstraEntry> pq = new PriorityQueue<GraphUtils.DijkstraEntry>();
 
         dist.put(source, 0.0);
         predecessor.put(source, null);
-        pq.add(new DijkstraEntry(0.0, source));
+        pq.add(new GraphUtils.DijkstraEntry(0.0, source));
 
         Set<String> visited = new HashSet<String>();
 
         while (!pq.isEmpty()) {
-            DijkstraEntry entry = pq.poll();
+            GraphUtils.DijkstraEntry entry = pq.poll();
             double entryDist = entry.distance;
             String current = entry.vertex;
 
@@ -210,7 +210,7 @@ public PathResult findShortestByWeight(String source, String target) {
                     predecessor.put(neighbor, current);
                     predecessorEdge.put(neighbor, e);
 
-                    pq.add(new DijkstraEntry(newDist, neighbor));
+                    pq.add(new GraphUtils.DijkstraEntry(newDist, neighbor));
                 }
             }
         }
@@ -282,29 +282,6 @@ public boolean areConnected(String source, String target) {
         return false;
     }
 
-    // --- Dijkstra priority-queue entry ---
-
-    /**
-     * Typed PQ entry replacing the previous {@code double[]} hack that required
-     * a parallel {@code vertexIndex} list and {@code vertexToIndex} map for
-     * int-to-vertex lookups. This eliminates the O(V) index bookkeeping and
-     * the fragile double-to-int casting on every PQ poll.
-     */
-    private static final class DijkstraEntry implements Comparable<DijkstraEntry> {
-        final double distance;
-        final String vertex;
-
-        DijkstraEntry(double distance, String vertex) {
-            this.distance = distance;
-            this.vertex = vertex;
-        }
-
-        @Override
-        public int compareTo(DijkstraEntry other) {
-            return Double.compare(this.distance, other.distance);
-        }
-    }
-
     // --- private helpers ---
 
     private void validateVertex(String vertex, String name) {