Assignment 10: mst solve

10-labMST/Assignment.java

@@ -71,7 +71,42 @@ public class Assignment {
     // of every vertex in the resulting tree. Other fields of QNode are optional
     // but may be useful in your implementation.
     public static List<QNode> Prim(Graph g) {
-        return new ArrayList<QNode>(Collections.nCopies(g.getLength(), new QNode()));
+        // Initialize the QNode list
+        List<QNode> qNodes = new ArrayList<>(g.getLength());
+        for (int i = 0; i < g.getLength(); i++) {
+            qNodes.add(new QNode());
+            qNodes.get(i).id = i;
+            // Set key to max value for lowest priority
+            qNodes.get(i).key = Integer.MAX_VALUE;
+        }
+
+        // Start from the first vertex
+        qNodes.get(0).key = 0;
+
+        // Priority queue to select the vertex with the minimum key as the next to be added to the MST
+        PriorityQueue<QNode> pq = new PriorityQueue<>(Comparator.comparingInt(qNode -> qNode.key));
+        // Add the first vertex to the priority queue
+        pq.add(qNodes.get(0));
+
+        while (!pq.isEmpty()) {
+            // Get the vertex with the minimum key
+            QNode u = pq.poll();
+            // Mark it as part of the MST
+            u.isValid = false;
+
+            // For each adjacent vertex,
+            // if it is not already in the MST and the weight is less than the current key
+            // update the key and parent (pi)
+            for (int v : g.getAdjacent(u.id)) {
+                if (qNodes.get(v).isValid && g.getWeight(u.id, v) < qNodes.get(v).key) {
+                    qNodes.get(v).key = g.getWeight(u.id, v);
+                    qNodes.get(v).pi = u.id;
+                    pq.add(qNodes.get(v));
+                }
+            }
+        }
+
+        return qNodes;
     }
 
     public static void run(String inputPath) {