Kruskal.java

package Kruskal;
import java.util.Arrays;
class Graph {  
    class Edge implements Comparable<Edge>{
           int src,dest,weight;
           public int compareTo(Edge e){
                return this.weight-e.weight;
            }
    }
    
	class subset{
        int parent,rank;
    }
    
    int E,V;
    Edge edge[];
    
    Graph(int v,int e){
        V=v;
        E=e;
        edge= new Edge[e];
        for(int i=0;i<e;i++){
            edge[i]= new Edge();
        }
    }
    
    int find(subset subsets[],int i){
        if(subsets[i].parent!=i){
            subsets[i].parent=find(subsets,subsets[i].parent);
        }
        return subsets[i].parent;
    }
   
   
    void Union(subset subsets[], int x, int y){
        int xroot = find(subsets, x);
        int yroot = find(subsets, y);
 // Attach smaller rank tree under root of high rank tree
        if (subsets[xroot].rank < subsets[yroot].rank)
            subsets[xroot].parent = yroot;
        else if (subsets[xroot].rank > subsets[yroot].rank)
            subsets[yroot].parent = xroot;
 
        // If ranks are same, then make one as root and increment
        // its rank by one
        else
        {
            subsets[yroot].parent = xroot;
            subsets[xroot].rank++;
        }
    }
    void KruskalMST(){
           // Edge Array to store result  
        Edge[] result = new Edge[V];
        for(int i=0;i<V;i++){
            result[i]= new Edge();
        }
        int e = 0;  // An index variable, used for result[]
        int i = 0;  // An index variable, used for sorted edges
        Arrays.sort(edge);
        // create V subsets
        subset subsets[]=new subset[V];
        for(i=0;i<V;i++){
            subsets[i]=new subset();
            
        }
          for(int v=0;v<V;v++){
            subsets[v].parent=v;
            subsets[v].rank=0;    
        }
          i=0;  //index used to pick next edge 
          // number of edges must be V-1 in a Spanning Tree
         while(e<V-1){
            Edge next_edge = new Edge();
            next_edge = edge[i++];
       
            int x=find(subsets,next_edge.src);
            int y=find(subsets,next_edge.dest);
             if(x!=y){
                 result[e++]=next_edge;
                 Union(subsets,x,y);
            } 
        }
        // print out
        System.out.println("Following are the edges in the constructed MST");
        for (i = 0; i < e; ++i)
            System.out.println(result[i].src+" -- "+result[i].dest+" == "+
                               result[i].weight);
    }
    public static void main(String[] args) {
        int V = 4;  // Number of vertices in graph
        int E = 5;  // Number of edges in graph
        Graph graph = new Graph(V, E);
 
        // add edge 0-1
        graph.edge[0].src = 0;
        graph.edge[0].dest = 1;
        graph.edge[0].weight = 10;
 
        // add edge 0-2
        graph.edge[1].src = 0;
        graph.edge[1].dest = 2;
        graph.edge[1].weight = 6;
 
        // add edge 0-3
        graph.edge[2].src = 0;
        graph.edge[2].dest = 3;
        graph.edge[2].weight = 5;
 
        // add edge 1-3
        graph.edge[3].src = 1;
        graph.edge[3].dest = 3;
        graph.edge[3].weight = 15;
 
        // add edge 2-3
        graph.edge[4].src = 2;
        graph.edge[4].dest = 3;
        graph.edge[4].weight = 4;
 
        graph.KruskalMST();
    }
    
}