C++模板实现循环链表

        循环链表是另一种形式的链式存贮结构。它的特点是表中最后一个结点的指针域指向头结点，整个链表形成一个环。

循环链表分类:

（1）单循环链表——在单链表中，将终端结点的指针域NULL改为指向表头结点或开始结点即可。

（2）多重链的循环链表——将表中结点链在多个环上。

带头结点:

       判断空链表的条件是head==head->next;

尾指针:

       用尾指针rear表示的单循环链表对开始结点a1和终端结点an查找时间都是O(1)。而表的操作常常是在表的首尾位置上进行，因此，实用中多采用尾指针表示单循环链表。带尾指针的单循环链表可见下图。

注意：判断空链表的条件为rear==rear->next;

特点:

循环链表的特点是无须增加存储量，仅对表的链接方式稍作改变，即可使得表处理更加方便灵活。

使用C++模板实现简单的循环链表：

ListNode.h

template<typename Type> class CircularList;

template<typename Type> class ListNode{
private:
friend class CircularList<Type>;
ListNode():m_pnext(NULL){}
ListNode(const Type item,ListNode<Type> *next=NULL):m_data(item),m_pnext(next){}
~ListNode(){
m_pnext=NULL;
}

private:
Type m_data;
ListNode *m_pnext;
};

CircularList.h

#include "ListNode.h"

template<typename Type> class CircularList{
public:
CircularList():head(new ListNode<Type>()){
head->m_pnext=head;
}
~CircularList(){
MakeEmpty();
delete head;
}
public:
void MakeEmpty();	//clear the list
int Length();		//get the length
ListNode<Type> *Find(Type value,int n);	//find the nth data which is equal to value
ListNode<Type> *Find(int n);			//find the nth data
bool Insert(Type item,int n=0);			//insert the data into the nth data of the list
Type Remove(int n=0);					//delete the nth data
bool RemoveAll(Type item);				//delete all the datas which are equal to value
Type Get(int n);	//get the nth data
void Print();		//print the list

private:
ListNode<Type> *head;

};

template<typename Type> void CircularList<Type>::MakeEmpty(){
ListNode<Type> *pdel,*pmove=head;
while(pmove->m_pnext!=head){
pdel=pmove->m_pnext;
pmove->m_pnext=pdel->m_pnext;
delete pdel;
}
}

template<typename Type> int CircularList<Type>::Length(){
ListNode<Type> *pmove=head;
int count=0;
while(pmove->m_pnext!=head){
pmove=pmove->m_pnext;
count++;
}
return count;
}

template<typename Type> ListNode<Type>* CircularList<Type>::Find(int n){
if(n<0){
cout<<"The n is out of boundary"<<endl;
return NULL;
}
ListNode<Type> *pmove=head->m_pnext;
for(int i=0;i<n&&pmove!=head;i++){
pmove=pmove->m_pnext;
}
if(pmove==head){
cout<<"The n is out of boundary"<<endl;
return NULL;
}
return pmove;
}

template<typename Type> ListNode<Type>* CircularList<Type>::Find(Type value,int n){
if(n<1){
cout<<"The n is illegal"<<endl;
return NULL;
}
ListNode<Type> *pmove=head;
int count=0;
while(count!=n){
pmove=pmove->m_pnext;
if(pmove->m_data==value){
count++;
}
if(pmove==head){
cout<<"can't find the element"<<endl;
return NULL;
}
}
return pmove;
}

template<typename Type> bool CircularList<Type>::Insert(Type item, int n){
if(n<0){
cout<<"The n is out of boundary"<<endl;
return 0;
}
ListNode<Type> *pmove=head;
ListNode<Type> *pnode=new ListNode<Type>(item);
if(pnode==NULL){
cout<<"Application error!"<<endl;
exit(1);
}
for(int i=0;i<n;i++){
pmove=pmove->m_pnext;
if(pmove==head){
cout<<"The n is out of boundary"<<endl;
return 0;
}
}

pnode->m_pnext=pmove->m_pnext;
pmove->m_pnext=pnode;
return 1;
}

template<typename Type> bool CircularList<Type>::RemoveAll(Type item){
ListNode<Type> *pmove=head;
ListNode<Type> *pdel=head->m_pnext;
while(pdel!=head){
if(pdel->m_data==item){
pmove->m_pnext=pdel->m_pnext;
delete pdel;
pdel=pmove->m_pnext;
continue;
}
pmove=pmove->m_pnext;
pdel=pdel->m_pnext;
}
return 1;
}

template<typename Type> Type CircularList<Type>::Remove(int n){
if(n<0){
cout<<"can't find the element"<<endl;
exit(1);
}
ListNode<Type> *pmove=head,*pdel;
for(int i=0;i<n&&pmove->m_pnext!=head;i++){
pmove=pmove->m_pnext;
}
if(pmove->m_pnext==head){
cout<<"can't find the element"<<endl;
exit(1);
}
pdel=pmove->m_pnext;
pmove->m_pnext=pdel->m_pnext;
Type temp=pdel->m_data;
delete pdel;
return temp;
}

template<typename Type> Type CircularList<Type>::Get(int n){
if(n<0){
cout<<"The n is out of boundary"<<endl;
exit(1);
}
ListNode<Type> *pmove=head->m_pnext;
for(int i=0;i<n;i++){
pmove=pmove->m_pnext;
if(pmove==head){
cout<<"The n is out of boundary"<<endl;
exit(1);
}
}
return pmove->m_data;
}

template<typename Type> void CircularList<Type>::Print(){
ListNode<Type> *pmove=head->m_pnext;
cout<<"head";
while(pmove!=head){
cout<<"--->"<<pmove->m_data;
pmove=pmove->m_pnext;
}
cout<<"--->over"<<endl<<endl<<endl;
}

Main.cpp

#include <iostream>
#include "CircularList.h"

using namespace std;

int main()
{
CircularList<int> list;
for(int i=0;i<20;i++){
list.Insert(i*3,i);
}
cout<<"the Length of the list is "<<list.Length()<<endl;
list.Print();
for(int i=0;i<5;i++){
list.Insert(3,i*3);
}
cout<<"the Length of the list is "<<list.Length()<<endl;
list.Print();

list.Remove(5);
cout<<"the Length of the list is "<<list.Length()<<endl;
list.Print();

list.RemoveAll(3);
cout<<"the Length of the list is "<<list.Length()<<endl;
list.Print();

cout<<"The third element is "<<list.Get(3)<<endl;

list.MakeEmpty();
cout<<"the Length of the list is "<<list.Length()<<endl;
list.Print();

return 0;
}