// A Java Program to detect cycle in a graph
import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;
class Graph {
private final int V;
private final List<List<Integer>> adj;
public Graph(int V)
{
this.V = V;
adj = new ArrayList<>(V);
for (int i = 0; i < V; i++)
adj.add(new LinkedList<>());
}
// This function is a variation of DFSUtil() in
// https://www.geeksforgeeks.org/archives/18212
private boolean isCyclicUtil(int i, boolean[] visited,
boolean[] recStack)
{
// Mark the current node as visited and
// part of recursion stack
if (recStack[i])
return true;
if (visited[i])
return false;
visited[i] = true;
recStack[i] = true;
List<Integer> children = adj.get(i);
for (Integer c: children)
if (isCyclicUtil(c, visited, recStack))
return true;
recStack[i] = false;
return false;
}
private void addEdge(int source, int dest) {
adj.get(source).add(dest);
}
// Returns true if the graph contains a
// cycle, else false.
// This function is a variation of DFS() in
// https://www.geeksforgeeks.org/archives/18212
private boolean isCyclic()
{
// Mark all the vertices as not visited and
// not part of recursion stack
boolean[] visited = new boolean[V];
boolean[] recStack = new boolean[V];
// Call the recursive helper function to
// detect cycle in different DFS trees
for (int i = 0; i < V; i++)
if (isCyclicUtil(i, visited, recStack))
return true;
return false;
}
// Driver code
public static void main(String[] args)
{
Graph graph = new Graph(4);
graph.addEdge(0, 1);
graph.addEdge(0, 2);
graph.addEdge(1, 2);
graph.addEdge(2, 0);
graph.addEdge(2, 3);
graph.addEdge(3, 3);
if(graph.isCyclic())
System.out.println("Graph contains cycle");
else
System.out.println("Graph doesn't "
+ "contain cycle");
}
}
// This code is contributed by Sagar Shah.