public class LeetCode24 {

	public static class ListNode {

		int val;

		ListNode next;

		ListNode(int x) {

			val = x;

		}

	}

	public ListNode swapPairs(ListNode head) {

		if (head == null || head.next == null) {

			return head;

		}

		ListNode cur = head;

		ListNode next = head;

		ListNode nextN = head;

		ListNode root = head.next;

		ListNode prev = null;

		while (cur != null) {

			if (cur.next == null) {

				prev.next = cur;

				break;

			}

			next = cur.next;

			nextN = next.next;

			next.next = cur;

			cur.next = null;

			if (prev != null) {

				prev.next = next;

			}

			prev = cur;

			cur = nextN;

		}

		return root;

	}

}