Prim’s algorithm in Java

Author: Deepali-Srivastava

Graph/prims/Demo.java

@@ -0,0 +1,48 @@
+/*
+Copyright (C) Deepali Srivastava - All Rights Reserved
+This code is part of DSA course available on CourseGalaxy.com    
+*/
+
+package prims;
+
+public class Demo 
+{
+	public static void main(String [] args)
+	{
+		UndirectedWeightedGraph g = new UndirectedWeightedGraph();
+
+		g.insertVertex("Zero");
+		g.insertVertex("One");
+		g.insertVertex("Two");
+		g.insertVertex("Three");
+		g.insertVertex("Four");
+		g.insertVertex("Five");
+		g.insertVertex("Six");
+		g.insertVertex("Seven");
+		g.insertVertex("Eight");
+		g.insertVertex("Nine");
+
+		g.insertEdge("Zero","One", 19);
+		g.insertEdge("Zero","Three", 14);
+		g.insertEdge("Zero","Four", 12); 
+		g.insertEdge("One","Two", 20); 
+		g.insertEdge("One","Four", 18); 
+		g.insertEdge("Two","Four", 17); 
+		g.insertEdge("Two","Five", 15);
+		g.insertEdge("Two","Nine", 29);
+		g.insertEdge("Three","Four", 13); 
+		g.insertEdge("Three","Six", 28); 
+		g.insertEdge("Four","Five", 16); 
+		g.insertEdge("Four","Six", 21); 
+		g.insertEdge("Four","Seven", 22);
+		g.insertEdge("Four","Eight", 24);
+		g.insertEdge("Five","Eight", 26); 
+		g.insertEdge("Five","Nine", 27); 
+		g.insertEdge("Six","Seven", 23); 
+		g.insertEdge("Seven","Eight", 30);
+		g.insertEdge("Eight","Nine", 35);
+
+		g.Prims();
+		
+	}
+}

Graph/prims/UndirectedWeightedGraph.java

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+/*
+Copyright (C) Deepali Srivastava - All Rights Reserved
+This code is part of DSA course available on CourseGalaxy.com    
+*/
+
+package prims;
+
+public class UndirectedWeightedGraph 
+{
+	public final int MAX_VERTICES = 30;
+
+	int n;           
+	int e;               
+    int [][] adj; 
+    Vertex [] vertexList;
+   
+    private static final int TEMPORARY = 1;
+    private static final int PERMANENT = 2;
+    private static final int NIL= -1;
+    private static final int INFINITY = 99999; 
+    
+   public UndirectedWeightedGraph()
+   {
+      adj = new int[MAX_VERTICES][MAX_VERTICES];
+      vertexList = new Vertex[MAX_VERTICES];
+   }
+   
+   public void Prims()
+   {	
+	    int c,v;
+	    
+	    int edgesInTree=0;
+	    int wtTree=0;
+   			    
+   		for(v=0; v<n; v++)
+   		{
+   			vertexList[v].status = TEMPORARY;
+   			vertexList[v].length = INFINITY;
+   			vertexList[v].predecessor = NIL;
+   		}
+
+   		int root=0;
+   		vertexList[root].length = 0;
+   		
+   		while(true)
+   		{
+   			c = tempVertexMinL();
+   	
+   			if(c == NIL) 
+   			{
+   				if(edgesInTree == n-1) 
+   				{
+   					System.out.println("Weight of minimum spanning tree is " + wtTree);
+   					return;
+   				}
+   				else 		
+   					throw new RuntimeException("Graph is not connected, Spanning tree not possible");
+   			}
+   		
+   			vertexList[c].status = PERMANENT;
+   			/* Include edge ( vertexList[c].predecessor,c ) in the tree*/ 
+   			if(c!=root)
+   			{
+   				edgesInTree++;
+   				System.out.println("(" + vertexList[c].predecessor + "," + c + ")");
+   				wtTree = wtTree + adj[vertexList[c].predecessor][c];
+   			}
+   			
+   			for(v=0; v<n; v++)
+   				if(isAdjacent(c,v) && vertexList[v].status == TEMPORARY)
+   					if(adj[c][v] < vertexList[v].length)
+   					{
+   						vertexList[v].length = adj[c][v];
+   						vertexList[v].predecessor = c;
+   					}
+   		}/*End of while*/
+ }
+
+   int tempVertexMinL()
+   {
+ 	 
+ 	 int min = INFINITY;
+ 	 int x = NIL;
+ 	
+ 	 for(int v=0; v<n; v++)
+ 	 {
+ 		if(vertexList[v].status == TEMPORARY && vertexList[v].length < min)
+ 		{
+ 			min=vertexList[v].length;
+ 			x=v;
+ 		}
+ 	 }
+ 	 return x;
+   }
+
+   private int getIndex(String s)
+   {
+	   for(int i=0; i<n; i++)
+	      if(s.equals(vertexList[i].name))
+	   		   return i;
+	   throw new RuntimeException("Invalid Vertex");
+   }
+   
+   public void insertVertex(String name)
+   {  
+	   vertexList[n++] = new Vertex(name);  
+   }
+   
+   private boolean isAdjacent(int u, int v)
+   {
+	   return (adj[u][v]!=0);
+   }
+   
+   /*Insert an edge (s1,s2) */
+   public void insertEdge(String s1, String s2, int wt)
+   {
+	  int u = getIndex(s1);
+	  int v = getIndex(s2);
+      if(adj[u][v] !=0 )
+    	  System.out.print("Edge already present");
+      else  
+      {
+         adj[u][v]=wt;
+         adj[v][u]=wt;
+         e++;
+      }
+   }
+}

Graph/prims/Vertex.java

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+/*
+Copyright (C) Deepali Srivastava - All Rights Reserved
+This code is part of DSA course available on CourseGalaxy.com    
+*/
+
+package prims;
+
+public class Vertex 
+{
+	String name;
+	int status;
+	int predecessor;
+	int length;
+		
+	Vertex(String name)
+	{
+		this.name = name;
+	}
+	public String toString()
+	{
+	     return name;
+	}
+}