c++ solution beats 100% of submission

[technoflinger]

    ListNode* swapPairs(ListNode* head) {
        
        if (NULL == head)
            return NULL;
        
        if (NULL == head->next)
            return head;
        
        ListNode* even = head;
        ListNode* odd = head->next;
        even->next = odd->next;
        odd->next = even;
        ListNode* newHead = odd;

        while (even->next && odd->next && even->next->next && odd->next->next)
        {
            ListNode* temp = even;
            even = even->next;
            odd = even->next;
            even->next = odd->next;
            odd->next = even;
            temp->next = odd;
        }
        return newHead;   
    }
};