雙向鏈表又稱為雙鏈表，使用雙向鏈表的目的是為了解決在鏈表中訪問直接前驅和后繼的問題。其設置前驅后繼指針的目的，就是為了節省其時間開銷，也就是用空間換時間。
在雙向鏈表的每個節點中應有兩個鏈接指針作為它的數據成員：pred指向其前驅節點，next指向其后繼節點。再加上數據域，因此每個雙向鏈表至少包括三個域。
實現代碼如下
//header.h
#include<iostream>
using namespace std;
/*
* 雙向循環鏈表頭文件，
* 其聲明中封裝有指向鏈表附加頭節點的頭x指針first
*/
template<class T>
struct DbNode
{
T data;
DbNode<T> *pred, *next;
DbNode(T value, DbNode<T> *a = NULL, DbNode<T> *b = NULL):\
data(value), pred(a), next(b){}
DbNode(DbNode<T> *a = NULL, DbNode<T> *b = NULL):pred(a), next(b){}
};
template<class T>
class Dblist
{
private: DbNode<T> *first;
public:
Dblist(T value);
~Dblist(){makeEmpty();}
void makeEmpty();
int Length()const;
bool IsEmpty(){return (this->first->pred == this->pred);}
DbNode<T> *getHead()const{return this->first;}
DbNode<T> *Locate(int i, int d);
DbNode<T> *Search(const T& x);
bool Insert(int i, const T& x, int d);
bool Remove(int i, T& x, int d);
void Print(int d);
};
template<class T>
int Dblist<T>::Length()const
{
DbNode<T> *tmp = this->first;
int i = 1;
while(tmp->next!=this->first)
{
++i;
tmp = tmp->next;
}
return i;
}
template<class T>
bool Dblist<T>::Remove(int i, T& x, int d)
{
DbNode<T> *p = this->Locate(i, d);
if(!p)
return false;
x = p->data;
if(p==this->first && this->Length()>1)
this->first = p->next;
else
cout<<"僅有頭節點的雙向循環鏈表已被刪除！請勿在沒添加新元素前對其調用。"<<endl;
p->pred->next = p->next;
p->next->pred = p->pred;
delete p;
return true;
}
template<class T>
DbNode<T>* Dblist<T>::Search(const T& x)
{
DbNode<T> *tmp = this->first;
do
{
if(tmp->data==x)
{
cout<<"address of x is "<<tmp<<" x = "<<tmp->data<<endl;
return tmp;
}
tmp = tmp->pred;
}while(tmp!=this->first);
return NULL;
}
template<class T>//定位元素，d=0時從頭節點向前(pred)查第i個元素，d!=0時，從頭節點向后(next)找第i個元素
DbNode<T>* Dblist<T>::Locate(int i, int d)
{
if(this->first->next==this->first || i==0)
return this->first;
int t = 1;
DbNode<T>* tmp = this->first;
if(d) //向后找
{
while(tmp->next!=this->first && t!=i)//查找到的條件為，在沒把雙向循環鏈表遍歷一遍前，t=i
{
tmp = tmp->next;
++t;
}
if(tmp->next==this->first&&t!=i)
return NULL;
else
return tmp;
}
else //向前找
{
while(tmp->pred!=this->first && t!=i)
{
tmp = tmp->pred;
++t;
}
if(tmp->pred==this->first&&t!=i)
return NULL;
else
return tmp;
}
}
template<class T>
bool Dblist<T>::Insert(int i, const T& x, int d)
{
DbNode<T> *p = this->Locate(i, d);
if(!p)
return false;
DbNode<T> *newnode = new DbNode<T>;
if(newnode==NULL)
{
cout<<"申請內存錯誤！"<<endl;
exit(1);
}
newnode->data = x;
if(d) //p節點后插入
{
p->next->pred = newnode;
newnode->pred = p;
newnode->next = p->next;
p->next = newnode;
}
else //p節點前插入
{
p->pred->next = newnode;
newnode->next = p;
newnode->pred = p->pred;
p->pred = newnode;
}
return true;
}
template<class T>
void Dblist<T>::makeEmpty()
{
DbNode<T> *p, *q = this->first->pred;
while(q != this->first)
{
p = q;
q = q->pred;
delete p;
}
}
template<class T>
void Dblist<T>::Print(int d)
{
if(d) //正序打印
{
cout<<"Positive order: ";
DbNode<T> *tmp = this->first;
while(tmp->next != this->first)
{
cout<<tmp->data<<"->";
tmp = tmp->next;
}
cout<<tmp->data<<"->over."<<endl;
}
else //逆序打印
{
DbNode<T> *tmp = this->first;
cout<<"Reverse sequence: ";
while(tmp->pred != this->first)
{
cout<<tmp->data<<"->";
tmp = tmp->pred;
}
cout<<tmp->data<<"->over."<<endl;
}
}
template<class T>
Dblist<T>::Dblist(T value)
{
this->first = new DbNode<T>(value);
if(this->first == NULL)
{
cerr<<"內存分配錯誤！"<<endl;
exit(1);
}
this->first->next = this->first->pred = this->first;
}
//main.cpp
#include"header.h"
int main()
{
Dblist<int> dl(888);
dl.Print(0);
for(int i=1; i<=4; ++i)
{
dl.Insert(1, i, 0);
}
dl.Print(1);
int l = 999, k = 0;
dl.Insert(0, l, 0);
//int k = 0;
dl.Print(1);
dl.Remove(0, k, 0);
dl.Print(1);
k = 5;
dl.Search(k);
dl.Print(0);
return 0;
}
完成效果
