A Java Program to detect cycle in a graph

class GFG {

private final int V;
private final List<List<Integer>> adj;

public GFG(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)
{
GFG graph = new GFG(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");
}
}

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