"""
Definition of ListNode
class ListNode(object):
def __init__(self, val, next=None):
self.val = val
self.next = next
"""
class Solution:
"""
@param: head: n
@return: The new head of reversed linked list.
"""
def reverse(self, head):
# write your code here
pre = None
while head:
temp = head.next
head.next = pre
pre = head
head = temp
return pre