题意：反转一个单链表。

示例: 输入: 1->2->3->4->5->NULL 输出: 5->4->3->2->1->NULL

一开始需要

cur = head
pre = None

第二步反转指针

cur.next = pre

 

接着再继续移动指针

tmp = cur.next // 放在反转之前
pre = cur
cur = tmp

 

完整代码

# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution(object):
    def reverseList(self, head):
        """
        :type head: ListNode
        :rtype: ListNode
        """
        cur = head
        pre = None

        while cur:
            tmp = cur.next
            cur.next = pre
            pre = cur
            cur = tmp
        
        return pre