comefrom: <qiyuangong>876_Middle_of_the_Linked_List_2.py
code: def middleNode( head):
      fast = slow = head
      while fast and fast.next:
          slow = slow.next
          fast = fast.next.next
      return slow
masked: def sample_funcname ( var_0 ) :
      var_2 = var_1 = var_0
      while var_2 and var_2.next :
          var_1 = var_1.next
          var_2 = var_2.next.next
      return var_1
  