public class DetectLoopExistance<E> {

    private Node<E> first;
    private Node<E> last;

    public void add(E element) {
        final Node<E> l = last;
        final Node<E> newNode = new Node<E>(element, null);
        last = newNode;
        if (first == null) {
            first = newNode;
        } else {
            l.next = newNode;
        }
    }

    private static class Node<E> {
        E element;
        Node<E> next;

        Node(E element, Node<E> next) {
            this.element = element;
            this.next = next;
        }
    }


    public boolean hasLoop() {
        Node<E> fast = first;
        Node<E> slow = first;

        while (fast != null && fast.next != null) {
            fast = fast.next.next;
            slow = slow.next;
            if (slow == fast) {
                return true;
            }
        }
        return false;
    }
   }

public boolean hasLoop() {
  Node<E> fast = first;
  Node<E> slow = first;

  while (fast != null && fast.next != null) {
    if (slow == fast.next || slow == fast.next.next) {
      return true;
    } else {
      fast = fast.next.next;
      slow = slow.next;
    }
  }
  return false;
}