线性表的链式实现

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再简单的数据结构都有实现的意义

线性表是最最基础的数据结构，因此我们需要高效地实现它，并用它为我们以后构建高效的数据结构提供帮助。

实现过程中的疑惑

有人建议笔者在表头处放置一个空的头结点，说是这样可以方便我们在最开始插入元素，但整个程序写下来，也没觉得方便了多少，因此下次准备不加试试。
类的封装性让我无法处理链表的归并。一开始，我的想法是类中的归并函数，接受一个List的对象，把两个对象归并，并把接受的对象的空间给销毁。但是，写起来的时候却发现，我并不能访问接受的对象的头指针，这样就没有办法进行归并了。
对链表进行排序，最优的算法就是归并排序了，时间上来说，O（nlogn）已经达到基于比较的排序算法的下限，空间上来说，这里又可以做到原地排序。但是，即使我实现了并归，链表的拆分还是没能成功调试。。。。。。。

#include <iostream>using namespace std;template <typename Key>struct Node{    Key key;    Node* next;};template <typename Key>class List{public:    List();    ~List();    void Clear();    bool IsEmpty()const    {        return ElemSize == 0;    }    int Length()const    {        return ElemSize;    }    bool IsContain(const Key& rhs)const;    Key Get(int index)const;    void Put(const Key& rhs,int index );    //Insert Element at the index of x    Key Delete(int index);                  //Delete the element at the index of x//    List Merge(List ) ;//？？？？？//    void Sort();    void Print()const;    void Reverse();    //iteratorprivate:    Node<Key>* head;    int ElemSize;};int main(){    List<int> MyList;    int a;    MyList.Put(1,0);    MyList.Put(2,0);    MyList.Put(3,0);    MyList.Put(4,0);    MyList.Put(5,2);    MyList.Print();    cout<<"The length of MyList is :"<<MyList.Length()<<endl;    cout<<"Index 1  :"<<MyList.Get(1)<<endl;    MyList.Delete(1);    cout<<"after delete at the index of 1:";    MyList.Print();    if(MyList.IsContain(3))        cout<<"It contains 3"<<endl;    if(MyList.IsContain(5))        cout<<"It contains 5"<<endl;    if(MyList.IsEmpty())        cout<<"It's empty1"<<endl;    MyList.Clear();    if(MyList.IsEmpty())        cout<<"It's empty2"<<endl;    cin>>a;    return 0;}template <typename Key>List<Key>::List(){    head = new Node<Key>;    head->next = NULL;    ElemSize = 0;}template <typename Key>List<Key>::~List(){    Node<Key>* p = head;    head = head->next;    while(head!=NULL)    {        delete(p);        p = head;        head = head->next;    }    delete(p);    ElemSize = 0;}template <typename Key>void List<Key>::Put(const Key& rhs,int index){    Node<Key>* p = head->next;    Node<Key>* pre = head;    Node<Key>* x = new Node<Key>;    x->key = rhs;    if(index>ElemSize||index<0)        throw "IndexError";    while(index-->0)    {        if(p!=NULL)        {            pre = p;            p = p->next;        }    }    x->next = pre->next;    pre->next = x;    ElemSize++;}template <typename Key>void List<Key>::Print()const{    Node<Key>* p = head->next;    while(p!=NULL)    {        cout<<p->key<<" ";        p = p->next;    }    if(ElemSize==0)        cout<<"NULL";    cout<<endl;}template <typename Key>void List<Key>::Reverse(){    Node<Key>* pre=NULL,*now=NULL,*next=NULL,*first=NULL;//Only change the node pointed by "now"    if(ElemSize<=1)        return ;    first = head;    pre = head->next;    now = pre->next;    next = now->next;    pre->next = NULL;    while(next!=NULL)    {        now->next = pre;        pre = now;        now = next;        next = next->next;    }    now->next = pre;    head->next = now;}template <typename Key>void List<Key>::Clear(){    Node<Key>* now = head->next->next;    Node<Key>* pre = head->next;    head->next = NULL;    while(now!=NULL)    {        delete(pre);        pre = now;        now = now->next;    }    delete(pre);    ElemSize = 0;}template <typename Key>bool List<Key>::IsContain(const Key& rhs)const{    Node<Key>* p = head->next;    while(p!=NULL&&p->key!=rhs)    p = p->next;    if(p==NULL)    return false;    else return true;}template <typename Key>Key List<Key>::Get(int index)const{    Node<Key>* p = head->next;    if(index>=ElemSize||index<0)        throw "IndexError";    while(index-->0&&p!=NULL)        p = p->next;    return p->key;}template <typename Key>Key List<Key>::Delete(int index){    Node<Key>* p = head;    Key key ;    if(index>=ElemSize||index<0)        throw "IndexError";    while(index-->0&&p->next!=NULL)    {        p = p->next;    }    Node<Key>* ToDe = p->next;    p->next = p->next->next;    key = ToDe->key;    delete(ToDe);    ElemSize--;    return key;}

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