一、206. 反转链表

• 代码：

class Solution:def reverseList(self, head):dummy = ListNode()cur = headwhile cur:last = cur.nextcur.next = dummy.nextdummy.next = curcur = lastreturn dummy.next

二、92. 反转链表 II

class Solution:def reverseBetween(self, head: Optional[ListNode], left: int, right: int) -> Optional[ListNode]:dummy = ListNode(next=head)new_head = dummyfor i in range(left-1):new_head = new_head.nextpre = None           cur = new_head.next  # 当前要反转的第一个元素for _ in range(right-left+1):nxt = cur.nextcur.next = prepre = curcur = nxtnew_head.next.next = curnew_head.next = prereturn dummy.next

三、25. K 个一组翻转链表

• 代码：

class Solution:def reverseKGroup(self, head: Optional[ListNode], k: int) -> Optional[ListNode]:# 统计节点个数n = 0cur = headwhile cur:n += 1cur = cur.nextp0 = dummy = ListNode(next=head)pre = Nonecur = head# k 个一组处理while n >= k:n -= kfor _ in range(k):  # 同 92 题nxt = cur.nextcur.next = pre  # 每次循环只修改一个 next，方便大家理解pre = curcur = nxt# 见视频nxt = p0.nextnxt.next = curp0.next = prep0 = nxtreturn dummy.next