PSListNode HasCycle(PSListNode pHead) {if ((NULL == pHead) || (NULL == pHead->pNextNode)){return NULL;}else{PSListNode pFast = pHead->pNextNode->pNextNode;PSListNode pSlow = pHead->pNextNode;//利用快慢指針，讓快指針每次走兩步，慢指針每次走一步，要是快指針沒有走到NULL，且快指針與慢指針指向相同就說明是有環while (pFast != pSlow){//快指針要是沒有指向為空，那么慢指針就不可能指向空（快指針走得快）if (NULL == pFast){return;}else{pFast = pFast->pNextNode;pSlow = pSlow->pNextNode; if (NULL == pFast){return;}else{pFast = pFast->pNextNode;}}}return pFast;} }int GetCyleLen(PSListNode pMeetNode) {//默認傳的參數是HasCycle函數返回的環中的一個結點if (NULL == pMeetNode){return 0;}else{int nCount = 1;PSListNode pNode = pMeetNode;while (pMeetNode != pNode->pNextNode){pNode = pNode->pNextNode;nCount++;}return nCount;} } //pMeetNode參數是用HasCycle函數求鏈表是否有環時pFast指針與pSlow指針的碰撞點 //定律：在鏈表頭，pFast指針與pSlow指針的碰撞點分別設定一個指針，每次各走一步，兩個指針必定相遇，則相遇第一點為環入口點 PSListNode FindEnterNode(PSListNode pHead, PSListNode pMeetNode) {PSListNode pNode = pHead;if ((NULL == pHead) || (NULL == pMeetNode)){return NULL;}while (pNode != pMeetNode){pNode = pNode->pNextNode;pMeetNode = pMeetNode->pNextNode;}return pNode; }

總結

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