定义一个函数,输入一个链表的头节点,反转该链表并输出反转后链表的头节点
示例:
输入: 1->2->3->4->5->NULL 输出: 5->4->3->2->1->NULL
双指针,需要记录当前结点的前置结点和后置结点
# Definition for singly-linked list. # class ListNode: # def __init__(self, x): # self.val = x # self.next = None class Solution: def reverseList(self, head: ListNode) -> ListNode: pre=None if not head: return None while head!=None: last=head.next head.next=pre pre=head head=last return pre