循环双链表

#include<iostream>
using namespace std;
struct LinkNode
{
   int value;
   LinkNode* next;
   LinkNode* pre;
};
LinkNode* createDoubleRoundLinkList()
{
    LinkNode* head = (LinkNode*)malloc(sizeof(LinkNode));
    head->next=head;
    head->pre=head;
    head->value=0;
    return head;
}

bool insertElem(int pos,int value,LinkNode* head)
{
    if(pos<=0)return 0;

    LinkNode* p = head;
    int j=0;
    while(p->next!=head && j<pos-1)//任然定位到pos-1的元素，也就是待插入元素的位置前一个，其实书上写的是到POS位置，但这样不能插在末尾了
    {                                
         p=p->next;
         j++;
    }
    if(j==pos-1)
    {
        LinkNode* newNode = (LinkNode*)malloc(sizeof(LinkNode));
        newNode->value=value;
        newNode->next=p->next;
        p->next=newNode;
        newNode->pre=p;
        if(newNode->next)//针对在链表末端的一个边界
            newNode->next->pre=newNode;
        head->value++;
        return 1;
    }
    return 0;
}
bool deleElem(int pos,LinkNode* head)
{
    if(pos<=0)return 0;
    LinkNode* p = head;
    int j=0;
    while(p->next!=head && j<pos)
    {
        p=p->next;
        j++;
    }
    if(j==pos)//这里可以定位到pos的元素，也就是待删除元素的位置,这里通过j==pos判断出合法情况，之所以不用p==head原因和循环单链表的一样
    {
        p->pre->next=p->next;
        p->next->pre=p->pre;//p->next不会为空
        delete(p);
        head->value--;
        return 1;
    }
    return 0;
}
void clearLinkList(LinkNode* head)
{
    LinkNode*p = head->next;
    while(p!=head) 
    {
        LinkNode* q = p->next;
        deleElem(1,head);//每次删除第一个，逐个删除
        p=q;
    }
}

void destroyLinkList(LinkNode* head)
{
   clearLinkList(head);
   delete head;
   head = 0;
}

void outPut(LinkNode* head)
{
    if(head == NULL)
    {
       cout<<"link list dose not exist"<<endl;
       return;
    }
    if(head->value==0)
    {
        cout<<"link list is empty"<<endl;
        return;
    }
    LinkNode* p = head->next;
    while(p!=head)
    {
         cout<<p->value<<" ";
         p=p->next;
    }
    cout<<endl;
}


void main()
{
    int len=12;
    LinkNode* L= createDoubleRoundLinkList();
    int v;
    for(int i=0;i<len;i++)
    {
         v = rand() % 100;
         cout<<v<<" ";
         insertElem(1,v,L);//每次在链表尾部插入，使得输入的顺序和链表中的顺序相反
    }
    cout<<endl;
    outPut(L);
    destroyLinkList(L);
   //outPut(L);
    L= createDoubleRoundLinkList();
    for(int i=0;i<len;i++)
    {
         v = rand() % 100;
         cout<<v<<" ";
         insertElem(L->value+1,v,L);//每次在链表尾部插入，使得输入的顺序和链表中的顺序一致

    }
    cout<<endl;
    outPut(L);
    insertElem(3,999,L);
    outPut(L);
    insertElem(100,999,L);
    outPut(L);
    insertElem(L->value,9999,L);
    outPut(L);
    insertElem(L->value+1,8888,L);
    outPut(L);
    insertElem(1,7777,L);
    outPut(L);
    deleElem(1,L);
    outPut(L);
    deleElem(100,L);
    outPut(L);
    deleElem(7,L);
    outPut(L);
    deleElem(L->value,L);
    outPut(L);
    deleElem(L->value+1,L);
    outPut(L);
    clearLinkList(L);
    outPut(L);
    insertElem(1,2,L);
    outPut(L);
    deleElem(L->value,L);
    outPut(L);
    cin>>len;
}