Leetcode: Swap Nodes in Pairs

http://oj.leetcode.com/problems/swap-nodes-in-pairs/

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode *swapPairs(ListNode *head) {
        // Note: The Solution object is instantiated only once and is reused by each test case.
        if(head==NULL) return NULL;
        if(head->next==NULL) return head;
        ListNode *newHead=head->next;
        ListNode *nextHead=newHead->next;
        newHead->next=head;
        head->next=swapPairs(nextHead);
        return newHead;
    }
};