PSListNode FindMidNode(PSListNode pHead)
{if (NULL == pHead){return NULL;}else{//快慢指针，快指针一次循环走两步，慢指针一次循环走一步PSListNode pSlow = pHead;PSListNode pFast = pHead;//注意结束条件得加上NULL != pFast->pNextNode，否则当NULL == pFast->pNextNode时，进入循环，//执行pFast = pFast->pNextNode->pNextNode时会崩溃while ((NULL != pFast) && (NULL != pFast->pNextNode)){pSlow = pSlow->pNextNode;pFast = pFast->pNextNode->pNextNode;}return pSlow;}
}