ListNode* MeetingNode(ListNode* pHead)

 {

     if(pHead==nullptr)

         return nullptr;

     ListNode* quickNode=pHead;

     ListNode* slowNode=pHead;

     while(quickNode->m_pNext!=nullptr&&quickNode->m_pNext->m_pNext!=nullptr)

     {

         quickNode=quickNode->m_pNext->m_pNext;

         slowNode=slowNode->m_pNext;

         if(quickNode==slowNode)

             break;

     }

     if(quickNode!=slowNode)

     {

         return nullptr;

     }

     return slowNode;

 }

 ListNode* EntryNodeOfLoop(ListNode* pHead)

 {

     ListNode* meetingNode=MeetingNode(pHead);

     if(meetingNode==nullptr)

         return nullptr;

     int nodesInLoop=;

     ListNode* pTemp=meetingNode;

     while(pTemp->m_pNext!=meetingNode)

     {

         pTemp=pTemp->m_pNext;

         nodesInLoop++;

     }

     ListNode* quickNode=pHead;

     ListNode* slowNode=pHead;

     for(int i=;i<nodesInLoop;i++)

         quickNode=quickNode->m_pNext;

     while(slowNode!=quickNode)

     {

         quickNode=quickNode->m_pNext;

         slowNode=slowNode->m_pNext;

     }

     return slowNode;

 }

 #include"List.h"

 void Test(char* testName,ListNode* pHead,ListNode* expect)

 {

     cout<<testName<<":";

     ListNode* result=EntryNodeOfLoop(pHead);

     if(result==nullptr)

     {

         cout<<"No loop in the link list."<<endl;

     }

     else if(result==expect)

     {

         cout<<"Passed."<<endl;

     }

     else

         cout<<"Failed."<<endl;

 }

 void Test1_7()

 {

     ListNode* pNode1=CreateListNode();

     ConnectListNodes(pNode1,pNode1);

     Test("test1",pNode1,pNode1);

     ListNode* pNode2=CreateListNode();

     ListNode* pNode3=CreateListNode();

     ListNode* pNode4=CreateListNode();

     ListNode* pNode5=CreateListNode();

     ListNode* pNode6=CreateListNode();

     ConnectListNodes(pNode1,pNode2);

     ConnectListNodes(pNode2,pNode3);

     ConnectListNodes(pNode3,pNode4);

     ConnectListNodes(pNode4,pNode5);

     ConnectListNodes(pNode5,pNode6);

     ConnectListNodes(pNode6,pNode3);

     Test("test2",pNode1,pNode3);

     ConnectListNodes(pNode6,pNode6);

     Test("test3",pNode1,pNode6);

     Test("test4",nullptr,nullptr);

     ConnectListNodes(pNode6,nullptr);

     Test("test5",pNode1,nullptr);

     DestroyList(pNode1);//注意销毁所定义的指针和链表

 }

 int main()

 {

     Test1_7();

     return ;

 }