aaa

/**
 * Definition for singly-linked list.
 * class ListNode {
 *     public int val;
 *     public ListNode next;
 *     ListNode(int x) { val = x; next = null; }
 * }
 */
public class Solution {
    public ListNode detectCycle(ListNode a) {
        if(a == null){
            return null;
        }

        if(a.next == null){
            return null;
        }

        ListNode walker = a;
        ListNode runner = walker.next;
       // int count = 0;

        while(walker.next != null && runner.next.next != null){
            if(runner == walker || runner.next == walker){
                return walker;
            }

            walker = walker.next;
            runner = runner.next.next;
           // count++;

           // if(walker == runner){
           //     if(count % 2 == 0){
           //         return walker;
           //     } else{
           //         return walker.next;
           //     }
           // }
        }

        return null;
    }
}