合并两个排序的链表使之依然有序(不开辟新空间在原链表上操作的非递归版本)_不开辟新空间,合并两个有序表

    ListNode* Merge(ListNode* pHead1, ListNode* pHead2)
    {
        if ( NULL ==pHead1 )
            return pHead2;
        else if ( NULL == pHead2 )
            return pHead1;
        
        ListNode* pLessHead = NULL;
        ListNode* pGreaterHead = NULL;
        ListNode* pRet = NULL;					//注意保存"头"为了之后返回
        ListNode* pNext = NULL;
        
        if ( pHead1->val <= pHead2->val ){
            pLessHead = pHead1;
            pGreaterHead = pHead2;
        }
        else{
            pLessHead = pHead2;
            pGreaterHead = pHead1;
        }
        
        pRet = pLessHead;
        
		//仔细分析逻辑就会发现，不可能运行到 pLessHead为NULL
        while ( NULL != pGreaterHead ){
            if ( pLessHead->val <= pGreaterHead->val ){
                if ( NULL == pLessHead->next ){
                    pLessHead->next = pGreaterHead;