[Leetcode][python]Swap Nodes in Pairs/两两交换链表中的节点

class Solution(object):
    def swapPairs(self, head):
        """
        :type head: ListNode
        :rtype: ListNode
        """
        dummy = ListNode(-1)
        dummy.next = head
        temp = dummy 
        while temp.next and temp.next.next:
            node1 = temp.next  # node1是B
            node2 = temp.next.next  # node2是C
            temp.next = node2  # A指向C
            node1.next = node2.next  # B指向D
            node2.next = node1  # C指向B
            temp = temp.next.next  # 跳过两个
        return dummy.next