不带头结点的头插法和尾插法

可见：不带头指针的插入操作比较繁琐，尤其是尾插法，每次需要遍历链表找到尾节点，然后执行插入操作

typedef int DATA;
struct SNode
{
	DATA data;
	SNode *pNext;
};

SNode *g_pHead = NULL;


/* 不带头结点的尾插法和头插法 */
void AddHead(DATA d)
{
	SNode *p = (SNode *)malloc(sizeof(SNode));
	p->data = d;
	p->pNext = g_pHead; //新节点的后继
	g_pHead = p; //首结点
}

void  AddTail(DATA d)
{
	SNode *ptr = g_pHead;
	SNode *p = (SNode *)malloc(sizeof(SNode));
	p->data = d;
	p->pNext = NULL;
	if (!ptr) //第一次为空节点时
	{
		g_pHead = p;
		return;
	}
	while (ptr->pNext) //循环查找尾节点，然后插入
	{
		ptr = ptr->pNext;
	}
	ptr->pNext = p;

}