循环双链表基本操作

#include<iostream>
using namespace std;
typedef char ElemType;
typedef struct DNode
{
    ElemType data;
    struct DNode * prior;
    struct DNode * next;
}DLinkNode;

void CreateListF(DLinkNode *&L,ElemType a[],int n)//头插法建立
{
    DLinkNode *s;
    L = (DLinkNode*)malloc(sizeof(DLinkNode));//创建头结点
    L->next = NULL;
    for(int i = 0;i<n;i++)
    {
        s = (DLinkNode*)malloc(sizeof(DLinkNode));
        s->data = a[i];
        s->next = L->next;
        if( L->next != NULL )//s插入原始结点之前，头结点之后
            L->next->prior = s;
        L->next = s;
        s->prior = L;
    }
    s = L->next;
    while(s->next != NULL)
    {
        s = s->next;
    }//s指向尾结点
    s->next = L;
    L->prior =  s;
}

void CreateListR(DLinkNode *&L,ElemType a[],int n )//尾插法建立
{
    DLinkNode *s;
    DLinkNode *r;
    L = (DLinkNode*)malloc(sizeof(DLinkNode));
    L->next = NULL;
    r = L;//r始终指向尾结点
    for(int i = 0;i<n;i++)
    {
        s = (DLinkNode*)malloc(sizeof(DLinkNode));
        s->data = a[i];
        r->next = s;
        s->prior = r;
        r = s;
    }
    r->next = L;
    L->prior = r; 
}

void InitList(DLinkNode *&L)
{
    L = (DLinkNode*)malloc(sizeof(DLinkNode));
    L->next = L->prior = L;
}

void DestoryList(DLinkNode *&L)
{
    DLinkNode *pre = L;
    DLinkNode *p = L->next;
    while(p != L)
    {
        free(pre);
        pre = p;
        p = p->next;//pre /p 同步后移
    }
    free(pre);
}

bool ListEmpty(DLinkNode *L)
{
    return (L->next == L);
}

int ListLength(DLinkNode *L)
{
    int j = 0;
    DLinkNode *p = L;
    while(p->next != L)
    {
        j++;
        p = p->next;
    }
    return (j);
}

void DispList(DLinkNode *L)
{
    DLinkNode * p = L->next;
    while(p != L)
    {
        cout<<" "<<p->data;
        p = p->next;
    }
    cout<<endl;
}

bool GetElem(DLinkNode *L,int i ,ElemType &e)
{
    int j = 1;
    DLinkNode *p = L->next;
    if(i <= 0  || L->next == L)
    {
        return false;
    }
    if(i == 1)//i == 1 特殊情况
    {
        e = p->next->data;
        return true;
    }
    else    
    {
        while( j < i && p != L)
        {
            j ++;
            p = p->next;
        }
        if(p == L)//没有找到
        {
            return false;
        }
        else//找到第i个
        {
            e = p->data;
            return true;
        }
    }
}

int LocateElem(DLinkNode *L,ElemType e)
{
    DLinkNode * p = L->next;
    int j = 1;
    while( p != NULL && p->data != e)
    {
        j++;
        p = p->next;
    }
    if(p == NULL)//不存在，返回false
    {
        return false;
    }
    else
    {
        return (j);
    }
}

bool ListInsert(DLinkNode *&L,int i ,ElemType e)//插入第i个元素
{   
    int j = 1;
    DLinkNode *p = L;
    DLinkNode *s;
    if(i<0)
    {
        return false;
    }
    if(p->next == L)//若链表为空时
    {
        s = (DLinkNode*)malloc(sizeof(DLinkNode));
        s->data = e;
        p->next = s;
        s->next = p;
        p->prior = s;
        s->prior = p;
        return true;
    }
    else if(i == 1)//L不为空 i == 1
    {
        s = (DLinkNode *)malloc(sizeof(DLinkNode));
        s->data = e;
        s->next = p->next;
        p->next = s;
        s->next->prior = s;//结点s插入结点p之后
        s->prior->next = p;
        return true;
    }
    else//i !=1 
    {
        p = L->next;
        while(j < i-1 && p != L)
        {
            j++;
            p = p->next;
        }
        if(p == L)
        {
            return false;
        }
        else
        {
            s = (DLinkNode*)malloc(sizeof(DLinkNode));
            s->data = e;
            s->next = p->next;
            if(p->next != NULL)
            {
                p->next->prior = s;
            }
            s->prior = p;
            p->next = s;
            return true;
        }
    }
}

bool ListDelete(DLinkNode *&L,int i ,ElemType &e)
{
    DLinkNode *p = L;
    DLinkNode *q;
    int  j = 1;
    if(i <=0 || L->next == L)
    {
        return false;
    }
    if(i == 1)//i == 1 特殊情况处理
    {
        q = L->next;
        e = q->data;
        L->next = q->next;
        q->next->prior = L;
        free(q);
        return true;
    }
    else
    {
        p = L->next;
        while(j < i-1 && p != NULL)
        {
            j++;
            p = p->next;            
        }
        if(p == NULL)//未找到i-1 个结点
        {
            return false;
        }
        else//找到i-1 个结点
        {
            q = p->next;//q指向待删除结点
            if(q == NULL)//不存在要删除的结点
            {
                return 0;
            }
            e = q->data;//删除q
            p->next = q->next;
            if(p->next != NULL)
                p->next->prior = p;
            free(q);//释放q
            return true;
        }
    }
}

int main()
{
    DLinkNode *L;
    ElemType e;
    cout<<"循环双链表的基本运算"<<endl;
    InitList(L);
    ListInsert(L,1,'a');
    ListInsert(L,2,'b');
    ListInsert(L,3,'c');
    ListInsert(L,4,'d');
    ListInsert(L,5,'e');
    cout<<"Disp"<<endl;
    DispList(L);
    cout<<"Length is :"<<ListLength(L)<<endl;
    GetElem(L,3,e);
    cout<<"Index 3 is :"<<e<<endl;
    ListDelete(L,4,e);
    cout<<"Delete Index 4"<<endl;
    DispList(L);
    cout<<"Destory"<<endl;
    DestoryList(L);
    return 0;
}