python 两两交换链表中的节点 多种解法

class ListNode:
    def __init__(self, val=0, next=None):
        self.val = val
        self.next = next

def swapPairs(head):
    if not head or not head.next:
        return head
  
    # 交换第一个节点和第二个节点
    first_node = head
    second_node = head.next
  
    first_node.next = swapPairs(second_node.next)
    second_node.next = first_node
  
    return second_node

class ListNode:
    def __init__(self, val=0, next=None):
        self.val = val
        self.next = next

def swapPairs(head):
    dummy = ListNode(0)  # 创建虚拟头节点
    dummy.next = head
    prev = dummy
    
    while head and head.next:
        # 要交换的两个节点
        first_node = head
        second_node = head.next

        # 交换节点
        prev.next = second_node
        first_node.next = second_node.next
        second_node.next = first_node

        # 更新指针
        prev = first_node
        head = first_node.next
      
    return dummy.next

class ListNode:
    def __init__(self, val=0, next=None):
        self.val = val
        self.next = next

def swapPairs(head):
    dummy = ListNode(0)  # 创建虚拟头节点
    dummy.next = head
    prev = dummy
    
    while head and head.next:
        # 要交换的两个节点
        first_node = head
        second_node = head.next

        # 交换节点
        prev.next = second_node
        first_node.next = second_node.next
        second_node.next = first_node

        # 更新指针
        prev = first_node.next
        head = first_node.next.next
      
    return dummy.next