/**

* Definition for singly-linked list.

* class ListNode {

* int val;

* ListNode next;

* ListNode(int x) {

* val = x;

* next = null;

* }

* }

*/

/**

* Detection of a cycle/loop in a Singly-Linked List by using Two pointer approach specifically Fast and Slow pointers.

*/

public class CycleDetectionInLinkedList{

public ListNode detectCycle(ListNode head)

{

if(head==null || head.next==null)

return null;

ListNode slow = head;

ListNode fast = head;

while(fast!=null && fast.next!=null)

{

slow = slow.next;

fast = fast.next.next;

if(slow==fast)

{

break;

}

}

if(slow==fast)

{

slow = head;

while(slow!=fast)

{

slow = slow.next;

fast = fast.next;

}

return fast;

}

return null;

}

}