package graphs;

// Problem Title => Java program to check if there is a cycle in directed graph using DFS.

import java.util.ArrayList;

import java.util.LinkedList;

import java.util.List;

public class Graph_Problem_04_ii {

private final int V;

private final List<List<Integer>> adj;

public Graph_Problem_04_ii(int V) {

this.V = V;

adj = new ArrayList<>(V);

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

adj.add(new LinkedList<>());

}

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

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_Problem_04_ii graph = new Graph_Problem_04_ii(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");

}

}