LeetCode 24 Swap Nodes in Pairs

package leetcode_50;

/**
 * 
 * @author pengfei_zheng
 * 交换相邻节点
 */
public class Solution24 {
    public 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 n = head.next;
        head.next = swapPairs(head.next.next);
        n.next = head;
        return n;
    }
}