DetectCycle

public class DetectCycle {
	int time;

	public boolean hasCycle(List <Node> nodes) {
		time = 0;

		for (Node node: nodes) {
			if (node.color.equals(Color.White)) {
				if (dfsVisit(node)) {
					return true;
				}
			}
		}

		return false;
	}

	// has cycle, return true
	private boolean dfsVisit(Node node) {
		node.inTime = ++time;
		node.color = Color.Gray;

		for (Node u: node.adjs) {
			if (u.color.equals(Color.Gray)) {
				return true;
			}
			if (u.color.equals(Color.White)) {
				u.parent = node;
				if (dfsVisit(u)) {
					return true;
				}
			}
		}
		node.color = Color.Black;
		node.outTime = ++time;
		return false;
	}

	public static void main(String []argv) {
		Node n0 = new Node(0);
		Node n1 = new Node(1);
		Node n2 = new Node(2);
		n0.adjs.add(n1);
		n1.adjs.add(n2);
		n2.adjs.add(n0);

		List <Node> nodes = new ArrayList<Node>();
		nodes.add(n0);
		nodes.add(n1);
		nodes.add(n2);

		DetectCycle dc = new DetectCycle();

		System.out.println(dc.hasCycle(nodes));

		Node b0 = new Node(0);
		Node b1 = new Node(1);
		Node b2 = new Node(2);
		b0.adjs.add(b1);
		b0.adjs.add(b2);
		b1.adjs.add(b2);

		List <Node> nodes2 = new ArrayList<Node>();
		nodes.add(b0);
		nodes.add(b1);
		nodes.add(b2);

		System.out.println(dc.hasCycle(nodes2));
	}
}

enum Color {
	White, Gray, Black
}

class Node {
	int val;
	int inTime;
	int outTime;
	Color color;
	Set <Node> adjs;
	Node parent;

	public Node(int x) {
		val = x;
		inTime = 0;
		outTime = 0;
		color = Color.White;
		adjs = new HashSet<Node>();
		parent = null;
	}

	@Override
	public int hashCode() {
		final int prime = 31;
		int result = 1;
		result = prime * result + ((adjs == null) ? 0 : adjs.hashCode());
		result = prime * result + ((color == null) ? 0 : color.hashCode());
		result = prime * result + inTime;
		result = prime * result + outTime;
		result = prime * result + ((parent == null) ? 0 : parent.hashCode());
		result = prime * result + val;
		return result;
	}

	@Override
	public boolean equals(Object obj) {
		if (this == obj)
			return true;
		if (obj == null)
			return false;
		if (getClass() != obj.getClass())
			return false;
		Node other = (Node) obj;
		if (adjs == null) {
			if (other.adjs != null)
				return false;
		} else if (!adjs.equals(other.adjs))
			return false;
		if (color != other.color)
			return false;
		if (inTime != other.inTime)
			return false;
		if (outTime != other.outTime)
			return false;
		if (parent == null) {
			if (other.parent != null)
				return false;
		} else if (!parent.equals(other.parent))
			return false;
		if (val != other.val)
			return false;
		return true;
	}
}