interview prepare_list

 1 class ListNode:
 2     def __init__(self,x):
 3         self.val=x
 4         self.next=None
 5 
 6 class Solution:
 7     def reverse(self,head):
 8         if(head==None or head.next==None):
 9             return head
10         
11         cur=head
12         pre=None
13         while(cur):
14             next=cur.next
15             cur.next=pre
16             pre=cur
17             cur=next
18         return pre
19 
20     def print_list(self,head):
21         while(head):
22             print(head.val)
23             head=head.next
24 
25 
26 n1=ListNode(1)
27 n2=ListNode(2)
28 n3=ListNode(3)
29 n4=ListNode(4)
30 n5=ListNode(5)  
31 n1.next=n2
32 n2.next=n3
33 n3.next=n4
34 n4.next=n5
35 s=Solution() 
36 res=s.reverse(n1)
37 s.print_list(res)