new_contents: # Definition for singly-linked list.
  # class ListNode:
  #     def __init__(self, x):
  #         self.val = x
  #         self.next = None
  
  
  class Solution:
      # @param {ListNode} head
      # @return {ListNode}
  
      def reverseList(self, head):
          if head is None:
              return head
          helper = ListNode(0)
  
          def reverse_list(head):
              if head is None:
                  return head
              prev = reverse_list(head.next)
              if prev is None:
                  helper.next = head
              else:
                  head.next = None
                  prev.next = head
              return head
  
          reverse_list(head)
          return helper.next
  
subject: add solution for Reverse Linked List