一、206. 反轉鏈表

• 代碼：

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

二、92. 反轉鏈表 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  # 當前要反轉的第一個元素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 個一組翻轉鏈表

• 代碼：

class Solution:def reverseKGroup(self, head: Optional[ListNode], k: int) -> Optional[ListNode]:# 統計節點個數n = 0cur = headwhile cur:n += 1cur = cur.nextp0 = dummy = ListNode(next=head)pre = Nonecur = head# k 個一組處理while n >= k:n -= kfor _ in range(k):  # 同 92 題nxt = cur.nextcur.next = pre  # 每次循環只修改一個 next，方便大家理解pre = curcur = nxt# 見視頻nxt = p0.nextnxt.next = curp0.next = prep0 = nxtreturn dummy.next