new_contents: 
  # Definition for singly-linked list.
  # class ListNode:
  #     def __init__(self, x):
  #         self.val = x
  #         self.next = None
  
  class Solution:
      # @param head, a ListNode
      # @return a boolean
      def hasCycle(self, head):
          if head == None or head.next == None:
              return False
          slow = fast = head
          while fast and fast.next:
              slow = slow.next
              fast = fast.next.next
              if slow == fast:
                  return True
          return False
  
subject: Add 20150615 question.