如何利用双重指针实现链表操作

双重指针（也称为哑指针或哨兵节点）在链表操作中非常有用，特别是当需要简化边界条件处理、提高代码可读性和减少错误时。以下是使用双重指针实现链表操作的一些建议：

1. 合并两个有序链表：

class ListNode:     def __init__(self, val=0, next=None):         self.val = val         self.next = next  def mergeTwoLists(l1: ListNode, l2: ListNode) -> ListNode:     dummy = ListNode(-1)     current = dummy      while l1 and l2:         if l1.val < l2.val:             current.next = l1             l1 = l1.next         else:             current.next = l2             l2 = l2.next         current = current.next      if l1:         current.next = l1     elif l2:         current.next = l2      return dummy.next 

2. 删除链表中的重复元素：

def deleteDuplicates(head: ListNode) -> ListNode:     if not head or not head.next:         return head      dummy = ListNode(-1)     dummy.next = head     current = dummy     prev = dummy      while current.next and current.next.next:         if current.next.val == current.next.next.val:             while current.next and current.next.val == current.next.next.val:                 current = current.next             prev.next = current.next         else:             prev = current             current = current.next      return dummy.next 

3. 反转链表：

def reverseList(head: ListNode) -> ListNode:     prev = None     current = head      while current:         next_node = current.next         current.next = prev         prev = current         current = next_node      return prev 

4. 找到链表的中间节点：

def middleNode(head: ListNode) -> ListNode:     slow = head     fast = head      while fast and fast.next:         slow = slow.next         fast = fast.next.next      return slow 

5. 删除链表的倒数第k个节点：

def removeNthFromEnd(head: ListNode, k: int) -> ListNode:     dummy = ListNode(-1)     dummy.next = head     first = dummy     second = dummy      for _ in range(k):         first = first.next      while first:         first = first.next         second = second.next      second.next = second.next.next      return dummy.next 

这些示例展示了如何使用双重指针简化链表操作。在实际应用中，您可能需要根据具体需求调整代码。