思路:单链表返回中点.  快慢指针,pSLow一次运行1步,pFast一次跑两步,pFast指向结尾时候,此时pSlow正好是中点

typedef int ElemType;

struct sNode

{

ElemType data;

sNode *next;

};

sNode* FindListMiddleNode(sNode* HL)//带表头附加结点

{

if(!HL || !HL->next)//如果HL为空或者它根本没有数据结点,返回NULL

return NULL;

sNode *pSlow, *pFast;

pSlow = HL->next;

pFast = HL->next->next;

while(pFast && pFast->next)

{

  pSlow = pSlow->next;

pFast = pFast->next->next;//一次两步

}

return pSlow;//返回中点

}