# Definition for singly-linked list.
# class ListNode(object):
# def __init__(self, x):
# self.val = x
# self.next = None
class Solution(object):
def reverseList(self, head):
"""
:type head: ListNode
:rtype: ListNode
"""
if not head or not head.next:
return head
pre = None
cur = head
while cur:
next = cur.next
cur.next = pre
pre = cur
cur = next
return pre
# 递归解决
class Solution2(object):
def reverseList(self, head):
"""
:type head: ListNode
:rtype: ListNode
"""
if not head or not head.next:
return head
rhead = self.reverseList(head.next)
head.next.next = head
head.next = None
return rhead