原题
翻转一个链表
样例
给出一个链表1->2->3->null，这个翻转后的链表为3->2->1->null
解题思路
- 基础链表问题，同向双指针
- temp = head.next //让temp记住head.next指向的节点
- head.next = prev //剪短head与原来head.next之间的关系，将head.next指向prev
- prev指向head，即向前移动一步
- head指向temp，也是向前移动一步
- 方法二 Recursion
完整代码
# Definition for singly-linked list.
# class ListNode(object):
# def __init__(self, x):
# self.val = x
# self.next = None
# 方法一 ：Non-recursion
class Solution(object):
def reverseList(self, head):
"""
:type head: ListNode
:rtype: ListNode
"""
prev = None
while head:
temp = head.next
head.next = prev
prev = head
head = temp
return prev
# 方法二 ：Recursion
class Solution(object):
def reverseList(self, head):
"""
:type head: ListNode
:rtype: ListNode
"""
if head is None or head.next is None:
return head
next = self.reverseList(head.next)
head.next.next = head
head.next = None
return next
