#include<iostream.h>
//定義節點（數據對象）的接口
class Node
{
    //聲明list類為本類的友元類
    friend class list;
//私有成員 
private:              
    int Data;       //節點數據
    Node *previous; //前趨指針
    Node *next;     //后繼指針
};

//定義雙向鏈表list的接口聲明
class list
{
//私有成員 
private:     
    Node *Head;    //鏈表頭指針
    Node *Tail;    //鏈表尾指針
//定義接口函數
public:
    //構造函數
    list();
    //析構函數
    ~list();
    //從鏈表尾后添加數據
    void Build_HT(int Data);
    //從鏈表前頭添加數據
    void Build_TH(int Data);
    //從頭到尾顯示數據
    void list::Display_HT();
    //從尾到頭顯示數據
    void list::Display_TH();
    //清除鏈表的全部數據
    void Clear();
};

//main()函數測試雙向鏈表
int main(void)
{
    list list1;
    int i;
   
    //從尾添加數據
    cout<<"Add to the back of the list1:"<<endl;
    for (i=1;i<=20;i=i+2) {
        list1.Build_HT(i);
        cout<<i<<" ";
    }
    cout<<endl;

    //從頭添加數據
    cout<<"Add to the front of the list1:"<<endl;
    for (i=0;i<=20;i=i+2) {
        list1.Build_TH(i);
        cout<<i<<" ";
    }
    cout<<endl;

    //顯示鏈表
    list1.Display_HT();
    list1.Display_TH();

    return 0;
}
//list類函數的定義
//構造函數的定義
list::list()
{
     //初值
     Head=0;
     Tail=0;
}
//析構函數的定義
list::~list()
{
    Clear(); 
}
//從鏈表尾后添加數據
void list::Build_HT(int Data)
{
    Node *Buffer;

    Buffer=new Node;
    Buffer->Data=Data;
    if(Head==0)
    {
        Head=Buffer;
        Head->next=0;
        Head->previous=0;
    Tail=Head;
    }
    else
    {
        Tail->next=Buffer;
        Buffer->previous=Tail;
    Buffer->next=0;
        Tail=Buffer;
    }
}
//從鏈表前頭添加數據
void list::Build_TH(int Data)
{
    Node *NewNode;
    NewNode=new Node;
    NewNode->Data=Data;

    if(Tail==0)
    {
        Tail=NewNode;
    Tail->next=0;
        Tail->previous=0;
        Head=Tail;
    }
    else
    {
        NewNode->previous=0;
        NewNode->next=Head;
        Head->previous=NewNode;
        Head=NewNode;
    }
}
//從頭到尾顯示數據
void list::Display_HT()
{
    Node *TEMP;
    TEMP=Head;
    cout<<"Display the list from Head to Tail:"<<endl;
    while(TEMP!=0)
    {
        cout<<TEMP->Data<<" ";
        TEMP=TEMP->next;
    }
    cout<<endl;
}
//從尾到頭顯示數據
void list::Display_TH()
{
    Node *TEMP;
    TEMP=Tail;
    cout<<"Display the list from Tail to Head:"<<endl;
    while(TEMP!=0)
    {
        cout<<TEMP->Data<<" ";
        TEMP=TEMP->previous;
    }
    cout<<endl;
}
//清除鏈表的全部數據
void list::Clear()
{
    Node *Temp_head=Head;

    if (Temp_head==0) return;
    do
    {
        Node *TEMP_NODE=Temp_head;
        Temp_head=Temp_head->next;
        delete TEMP_NODE;
    }
    while (Temp_head!=0);
}