1def swapPairs(head):
2 dummy = ListNode(0)
3 dummy.next = head
4 prev = dummy
5
6 while prev.next and prev.next.next:
7 first = prev.next
8 second = first.next
9
10 # Swap the pair
11 prev.next = second
12 first.next = second.next
13 second.next = first
14
15 # Move to next pair
16 prev = first
17
18 return dummy.next