查找单链表的中间结点，要求只能遍历一次链表

pNode FindMiddleNode(pList plist)
{
	/*
	快慢指针，快的两步，慢的一步
	*/
	pNode pFast = plist;
	pNode pSlow = plist;
	while (pFast&&pFast->next)
	{
		pFast = pFast->next->next;
		pSlow = pSlow->next;
	}
	return pSlow;
}