cycle2

public class Solution {
    public ListNode detectCycle(ListNode head) {
        ListNode p1 = head;
        ListNode p2 = head;


        while(p2!=null&&p2.next!=null){
            p1=p1.next;
            p2=p2.next.next;
            if(p1==p2){
              break;
            }
        }
        if (p2 == null || p2.next == null){
        return null;
    }

        ListNode p3 = head;
        while(p3!= p2){
            p3=p3.next;
            p2=p2.next;

        }

        return p3;

    }
}