线性表之循环双链表

    在循环链表中，虽然从任一结点出发均可以扫描到其他结点，但是要找到其前驱结点则需要遍历整个链表。如果希望快速确定表中任一结点的前驱结点，可以再每个结点中再设置一个指向其前驱结点的指针域，这样就形成的双链表(doubly linked list)，如第一张图所示，prior为前驱指针域，next为后继指针域。

   结点的C++描述为：

template<class Type>struct DulNode{Type data;//数据域DulNode<Type> *prior, *next;        //指向前驱结点的指针和指向后继结点的指针};

    和单链表类似，双链表一般也是由头指针唯一确定，增加头结点也能使双链表的某些操作变得方便，将头结点和尾结点链接起来就构成了循环双链表，这样无论是插入还是删除操作，对链表中开始结点、终端结点和中间结点的操作过程相同。实际上常用带头结点的循环双链表，实现如下：

dullinklist类的声明：

template<class Type>class Dullist{private:DulNode<Type>* first;//头指针指向头结点public:Dullist();//显示默认构造函数Dullist(Type a [], int len);//构造函数~Dullist();//析构函数int getLength();//求双链表的长度Type Get(int i);//按位查找数据int Locate(Type x);//按值查找数据位置void Insert(int i, Type x);//在线性表第i个位置上插入值为x的结点Type Delete(int i);//删除第i个元素void Print();//遍历循环双链表bool isEqual();//判断循环双链表是否是对称};

类实现：

template<class Type>Dullist<Type>::Dullist(){first = new DulNode<Type>;first->next = first;first->prior = first;}template<class Type>Dullist<Type>::Dullist(Type a [], int len){first = new DulNode<Type>;first->next = first;first->prior = first;DulNode<Type>* r = first;for (int i = 0; i < len; i++){DulNode<Type>* s = new DulNode<Type>;s->data = a[i];r->next = s;s->prior = r;r = s;}r->next = first;first->prior = r;}template<class Type>Dullist<Type>::~Dullist(){int len = getLength();DulNode<Type>* p = first;while (len+1){p = first;first = first->next;delete p;len--;}}template<class Type>int Dullist<Type>::getLength(){int count = 0;DulNode<Type>* p = first->next;while (p != first){count++;p = p->next;}return count;}template<class Type>void Dullist<Type>::Print(){cout<< "头结点";DulNode<Type>* p =first->next;while (p != first){cout << "-->" << p->data;p = p->next;}cout << "-->头结点" << endl;}template<class Type>Type Dullist<Type>::Get(int i){int count = 1;DulNode<Type>* p = first->next;while (p != first&&count < i){count++;p = p->next;}if (p == first)throw"位置";else{return p->data;}}template<class Type>int Dullist<Type>::Locate(Type x){int count = 1;DulNode<Type>* p = first->next;while (p != first){if (p->data == x)return count;p = p->next;count++;}return 0;}template<class Type>void Dullist<Type>::Insert(int i, Type x){int count = 0;DulNode<Type>* p = first;while (count < i - 1){p = p->next;count++;}DulNode<Type>* s = new DulNode<Type>;s->data = x;s->prior = p;s->next = p->next;p->next->prior = s;p->next = s;}template<class Type>Type Dullist<Type>::Delete(int i){DulNode<Type>* p = first;int count = 0;while (count < i ){p = p->next;count++;}if (p == first)throw"位置";else{p->prior->next = p->next;p->next->prior = p->prior;delete p;}}template<class Type>bool Dullist<Type>::isEqual(){DulNode<Type>* p = first->next;DulNode<Type>* q = first->prior;while (p != q&&p->prior != q){if (p->data == q->data){p = p->next;q = q->prior;}else return false;}return true;}

main.cpp

#include "dullist.cpp"#include "dullist.h"int main(){int a[7] = { 1, 2, 3, 4,3,2,1 };Dullist<int> dl(a, 7);dl.Print();cout << "dl的长度是：" << dl.getLength() << endl;cout << "第6个结点是：" << dl.Get(6) << endl;cout << "4是第" << dl.Locate(4) << "个结点" << endl;dl.Insert(4, 10);cout << "在第四个位置上插入10：";dl.Print();dl.Delete(1);cout << "删除第1个结点：";dl.Print();cout << "dl" << (dl.isEqual() == true ? "是" : "不是") << "对称的" << endl;return 0;}

测试结果：