Swap Nodes in Pairs

1public ListNode swapPairs(ListNode head) {
2    ListNode dummy = new ListNode(0);
3    dummy.next = head;
4    ListNode prev = dummy;
5
6    while (prev.next != null && prev.next.next != null) {
7        ListNode first = prev.next;
8        ListNode 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
19    return dummy.next;
20}