链表_leetcode206

# 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