// Java Program for union-find algorithm to detect cycle in a graph

import java.util.*;

import java.lang.*;

import java.io.*;

class Graph

{

int V, E; // V-> no. of vertices & E->no.of edges

Edge edge[]; // /collection of all edges

class Edge

{

int src, dest;

};

// Creates a graph with V vertices and E edges

Graph(int v,int e)

{

V = v;

E = e;

edge = new Edge[E];

for (int i=0; i<e; ++i)

edge[i] = new Edge();

}

// A utility function to find the subset of an element i

int find(int parent[], int i)

{

if (parent[i] == -1)

return i;

return find(parent, parent[i]);

}

// A utility function to do union of two subsets

void Union(int parent[], int x, int y)

{

int xset = find(parent, x);

int yset = find(parent, y);

parent[xset] = yset;

}

// The main function to check whether a given graph

// contains cycle or not

int isCycle( Graph graph)

{

// Allocate memory for creating V subsets

int parent[] = new int[graph.V];

// Initialize all subsets as single element sets

for (int i=0; i<graph.V; ++i)

parent[i]=-1;

// Iterate through all edges of graph, find subset of both

// vertices of every edge, if both subsets are same, then

// there is cycle in graph.

for (int i = 0; i < graph.E; ++i)

{

int x = graph.find(parent, graph.edge[i].src);

int y = graph.find(parent, graph.edge[i].dest);

if (x == y)

return 1;

graph.Union(parent, x, y);

}

return 0;

}

// Driver Method

public static void main (String[] args)

{

/* Let us create following graph

0

| \

| \

1-----2 */

int V = 3, E = 3;

Graph graph = new Graph(V, E);

// add edge 0-1

graph.edge[0].src = 0;

graph.edge[0].dest = 1;

// add edge 1-2

graph.edge[1].src = 1;

graph.edge[1].dest = 2;

// add edge 0-2

graph.edge[2].src = 0;

graph.edge[2].dest = 2;

if (graph.isCycle(graph)==1)

System.out.println( "graph contains cycle" );

else

System.out.println( "graph doesn't contain cycle" );

}

}