I read through some answers and people have missed one obvious solution to the above problem.
If given we can change the structure of the class Node then we can add a boolean flag to know if it has been visited or not. This way we only traverse list once.
Class Node{ Data data; Node next; boolean isVisited;}public boolean hasLoop(Node head){ if(head == null) return false; Node current = head; while(current != null){ if(current.isVisited) return true; current.isVisited = true; current = current.next; } return false;}
