Create Prim's Algorithm

Author: rajatag03

Prim's Algorithm

@@ -0,0 +1,78 @@
+public class Main {
+    public static void main(String[] args) {
+        int noOfVertices = 5;
+        int startVertex=0;  // A is start vertex
+        
+        List<Pair<Integer,Integer>>[] adj=new ArrayList[noOfVertices];
+        
+        //Pair(vertex, weight)
+        List<Pair<Integer,Integer>> list=new ArrayList<>();
+        list.add(new Pair(1,4));
+        list.add(new Pair(2,1));
+        adj[0]=list;
+        
+        list=new ArrayList<>();
+        list.add(new Pair(0,4));
+        list.add(new Pair(2,2));
+        list.add(new Pair(4,4));
+        adj[1]=list;
+        
+        list=new ArrayList<>();
+        list.add(new Pair(0,1));
+        list.add(new Pair(1,2));
+        list.add(new Pair(3,4));
+        adj[2]=list;
+        
+        list=new ArrayList<>();
+        list.add(new Pair(2,4));
+        list.add(new Pair(4,4));
+        adj[3]=list;
+        
+        list=new ArrayList<>();
+        list.add(new Pair(1,4));
+        list.add(new Pair(3,4));
+        adj[4]=list;
+        
+        int[] path = new int[noOfVertices];
+        Pair<Integer,Integer>[] distance = new Pair[noOfVertices];
+        boolean[] mstset = new boolean[noOfVertices];
+        
+        // Intialize distance array
+        for(int i=0;i<noOfVertices;i++){
+            distance[i] = new Pair<Integer,Integer>(i,Integer.MAX_VALUE);
+        }
+        
+        distance[startVertex]=new Pair<>(startVertex,0); // Making distance for start vertex 0
+        path[startVertex]=startVertex; // Updating path for start vertex to itself
+        
+        PriorityQueue<Pair<Integer,Integer>> q=new PriorityQueue<>((a,b) -> a.getValue()-b.getValue());
+        q.add(distance[startVertex]);
+        
+        while(!q.isEmpty()){
+            Pair<Integer,Integer> vertexPair=q.remove();
+            Integer vertex=vertexPair.getKey();
+            mstset[vertex]=true;
+            
+            List<Pair<Integer,Integer>> adjVertices=adj[vertex];
+
+            for(Pair<Integer,Integer> adjPair: adjVertices){
+                int adjVertex=adjPair.getKey();
+                int weight=adjPair.getValue();
+                
+                int newDistance=distance[vertex].getValue() + weight;
+                if(!mstset[adjVertex] && distance[adjVertex].getValue() > newDistance){
+                    q.remove(distance[adjVertex]);
+                    distance[adjVertex]=new Pair<>(adjVertex,newDistance);
+                    path[adjVertex]=vertex;
+                    q.add(distance[adjVertex]);
+                }
+            }
+        }
+        
+        System.out.println("MST formed by edges :");
+        for(int i=0;i<noOfVertices; i++){
+            if(i!=startVertex)
+                System.out.println((char)(i+'A')+" - "+(char)(path[i]+'A'));
+        }
+    }    
+}