new_contents: """
  Detect a cycle in a linked list. Note that the head pointer may be 'None' if the list is empty.
  
  A Node is defined as: 
   
      class Node(object):
          def __init__(self, data = None, next_node = None):
              self.data = data
              self.next = next_node
  """
  
  
  def has_cycle(head):
      pass
subject: Add files via upload