leetcode Swap Nodes in Pairs

解决此题方法，每次选取两个node改变它们的位置，注意若最后只剩下一个元素则不需要改变位置

代码

class Solution {
public:
    ListNode *swapPairs(ListNode *head) {
        
        if(head==NULL||head->next==NULL)
            return head;
      
        ListNode *first, *second, *newHead, *p, *tempTail;
        
        newHead = new ListNode(0);
        tempTail = newHead;
        p = head;
    
        while(p!=NULL&&p->next!=NULL)
        {
            first = p;
            second = p->next;
            p = second->next;
            
            first->next = tempTail->next;
            tempTail->next = second;
            second->next = first;
            tempTail = first;
            
        }
        //将剩余的单个节点加上
        if(p!=NULL)
            tempTail->next = p;
        
        
        return newHead->next;
        
      
        
    }
};