Q4_2.java

import java.util.ArrayList;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.Queue;

public class Q4_2 {
	public static void main(String[] args) {
		NodeWithState nodea = new NodeWithState("a");
		NodeWithState nodeb = new NodeWithState("b");
		NodeWithState nodec = new NodeWithState("c");
		NodeWithState noded = new NodeWithState("d");
		nodea.nexts.add(nodeb);
		nodec.nexts.add(nodeb);
		noded.nexts.add(nodea);
		System.out.println(isConnected(nodea,noded));
	}

	static boolean isConnected(NodeWithState source, NodeWithState des) {
		if(source == des)
			return true;
		Queue<NodeWithState> q = new LinkedList<NodeWithState>();
		q.add(source);
		source.state = State.VISITING;
		while (!q.isEmpty()) {
			NodeWithState current = q.poll();
			if (current.nexts != null && current.nexts.size() != 0) {
				for (NodeWithState node : current.nexts) {
					if (des == node)
						return true;
					else if (node.state == State.UNVISITED) {
						node.state = State.VISITING;
						q.add(node);
					}
				}

			}
			current.state = State.VISITED;
		}
		return false;

	}
}

enum State {
	VISITED, VISITING, UNVISITED;
}

class NodeWithState {
	String value;
	ArrayList<NodeWithState> nexts;
	State state;

	NodeWithState(String val) {
		value = val;
		nexts = new ArrayList<NodeWithState>();
		state = State.UNVISITED;
	}
}