class ListNode: 
  def __init__(self,x): 
    self.val=x; 
    self.next=None; 
 
def nonrecurse(head):       #循环的方法反转链表 
  if head is None or head.next is None: 
    return head; 
  pre=None; 
  cur=head; 
  h=head; 
  while cur: 
    h=cur; 
    tmp=cur.next; 
    cur.next=pre; 
    pre=cur; 
    cur=tmp; 
  return h; 
   
head=ListNode(1);  #测试代码 
p1=ListNode(2);   #建立链表1->2->3->4->None; 
p2=ListNode(3); 
p3=ListNode(4); 
head.next=p1; 
p1.next=p2; 
p2.next=p3; 
p=nonrecurse(head);  #输出链表 4->3->2->1->None 
while p: 
  print p.val; 
  p=p.next; 

class ListNode: 
  def __init__(self,x): 
    self.val=x; 
    self.next=None; 
 
   
def recurse(head,newhead):  #递归，head为原链表的头结点，newhead为反转后链表的头结点 
  if head is None: 
    return ; 
  if head.next is None: 
    newhead=head; 
  else : 
    newhead=recurse(head.next,newhead); 
    head.next.next=head; 
    head.next=None; 
  return newhead; 
   
head=ListNode(1);        #测试代码 
p1=ListNode(2);         # 建立链表1->2->3->4->None 
p2=ListNode(3); 
p3=ListNode(4); 
head.next=p1; 
p1.next=p2; 
p2.next=p3; 
newhead=None; 
p=recurse(head,newhead);      #输出链表4->3->2->1->None 
while p: 
  print p.val; 
  p=p.next;