CODE

/**
* Definition for singly-linked list.
* public class ListNode {
*     public int val;
*     public ListNode next;
*     public ListNode(int val=0, ListNode next=null) {
*         this.val = val;
*         this.next = next;
*     }
* }
*/

public class Solution {
  List<ListNode> processedNodes = new List<ListNode>();

  public bool HasCycle(ListNode head) {
    while (head != null)
    {
      if (processedNodes.Contains(head.next))
        return true;
      else
        processedNodes.Add(head);
      head = head.next;
    }
    return false;
  }
}