package Graph;

import java.util.HashSet;

public class CycleDetection {

static HashSet<Integer> visited = new HashSet<>();

private static boolean detectCycle(Graph g) {

for (int i = 0; i < g.vertices; i++) {

if (cyclic(g, i, new HashSet<>()))

{

return true;

}

}

return false;

}

private static boolean cyclic(Graph g, int source, HashSet<Integer> curr) {

if (curr.contains(source)) return true;

if (visited.contains(source)) return false;

visited.add(source);

curr.add(source);

for (int item : g.adjacentList.get(source)) {

if (cyclic(g, item, curr))

{

return true;

}

}

return false;

}

public static void main(String args[]) {

Graph g1 = new Graph(4);

g1.addEdge(0,1);

g1.addEdge(1,2);

g1.addEdge(1,3);

g1.addEdge(3,0);

g1.printGraph();

System.out.println(detectCycle(g1));

System.out.println();

Graph g2 = new Graph(3);

g2.addEdge(0,1);

g2.addEdge(1,2);

g2.printGraph();

System.out.println(detectCycle(g2));

}

}