package LeetCode;

public class LeetCode24 {

    // 24. Swap Nodes in Pairs
    // https://leetcode.com/problems/swap-nodes-in-pairs/description/
    // : O(n)
    // : O(1)

    public ListNode swapPairs(ListNode head) {

        ListNode dummyHead = new ListNode(0);
        dummyHead.next = head;

        ListNode p = dummyHead;
        while(p.next != null && p.next.next != null ){
            ListNode node1 = p.next;
            ListNode node2 = node1.next;
            ListNode next = node2.next;
            node2.next = node1;
            node1.next = next;
            p.next = node2;
            p = node1;
        }

        return dummyHead.next;
    }
}