基于双向链表的list

Description

请实现以下基于双向链表的list类

enum Error_code{           success,           underflow,           overflow};template <class List_entry>struct Node{           List_entry entry;           Node<List_entry> *next;           Node<List_entry> *back;};template <class List_entry>class MyList{public:           MyList();           ~MyList();           // 拷贝构造函数和赋值运算符重载，注意深拷贝与浅拷贝的差异           MyList(const MyList<List_entry> &copy);           void operator =(const MyList<List_entry> &copy);           // 清空list           void clear();           // 判断list是否为空           bool empty() const;           // 判断list是否已满           bool full() const;           // 获取list的元素数量           int size() const;           // 在第position个位置插入值为entry的元素，如果position为0则插入在链表头，依次类推           // 若position < 0 或者 position > count，则返回underflow           Error_code insert(int position, const List_entry &entry);           // 删除第position个位置的元素，并将该元素的值保存在entry中           // 若position < 0 或者 position >= count，则返回underflow           Error_code remove(int position, List_entry &entry);           // 获取第position个位置的元素，保存在entry中           // 若position < 0 或者 position >= count，则返回underflow           Error_code retrieve(int position, List_entry &entry) const;           // 将第position个位置的元素替换为entry           // 若position < 0 或者 position >= count，则返回underflow           Error_code replace(int position, const List_entry &entry);           // 用visit函数遍历list内所有的元素           void traverse(void (*visit)(List_entry &));protected:           int count;                                                                          // 记录list内元素数量           mutable int curPosition;                                 // current指针的位置编号           mutable Node<List_entry> *current;                // current指针           // 设置current指针的位置，指向第position个位置           void setPosition(int position) const;};

注意，不需要提交main函数。

Input

None

Output

None

题解：

关于双向链表的构造并不难，注意要慎重处理链表的插入与删除操作，比如：向当前位置插入节点时，需要考虑当前位置之前是否存在节点；删除当前节点时，需要考虑当前位置之前以及之后是否存在节点。

Code

// Problem#: 20997// Submission#: 5187924// The source code is licensed under Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License// URI: http://creativecommons.org/licenses/by-nc-sa/3.0/// All Copyright reserved by Informatic Lab of Sun Yat-sen Universityenum Error_code{    success,    underflow,    overflow};template <class List_entry>struct Node{    List_entry entry;    Node<List_entry> *next;    Node<List_entry> *back;    Node<List_entry>() {entry = 0; next = NULL; back = NULL;}    Node<List_entry>(List_entry entry, Node<List_entry> * back,Node<List_entry> * next):entry(entry),back(back),next(next){}};template <class List_entry>class MyList{public:    MyList()    {        count = 0;        curPosition = -1;        current = 0;    }    ~MyList() { clear(); }    // 拷贝构造函数和赋值运算符重载，注意深拷贝与浅拷贝的差异    MyList(const MyList<List_entry> &copy)    {        if (copy.empty())        {            count = 0;            curPosition = -1;            current = 0;        }        else        {            int index = copy.curPosition;            Node<List_entry> * point = copy.current;            while(index!=0)            {                index--;                point = point->back;            }            count = copy.count;            current = new Node<List_entry>(point->entry,0,0);            while(point->next!=0)            {                point = point->next;                current->next = new Node<List_entry>(point->entry,current,0);                current = current->next;            }            curPosition = count-1;        }    }    void operator =(const MyList<List_entry> &copy)    {        clear();        if (copy.empty())        {            count = 0;            curPosition = -1;            current = 0;        }        else        {            int index = copy.curPosition;            Node<List_entry> * point = copy.current;            while(index!=0)            {                index--;                point = point->back;            }            count = copy.count;            current = new Node<List_entry>(point->entry,0,0);            while(point->next!=0)            {                point = point->next;                current->next = new Node<List_entry>(point->entry,current,0);                current = current->next;            }            curPosition = count-1;        }    }    // 清空list    void clear()    {        if (empty())        {            curPosition = -1;            current = 0;            return ;        }        List_entry tmp;        while(!empty()) remove(0,tmp);        curPosition = -1;        count = 0;        current = 0;    }    // 判断list是否为空    bool empty() const { return count==0; }    // 判断list是否已满    bool full() const { return false; }    // 获取list的元素数量    int size() const { return count; }    // 在第position个位置插入值为entry的元素，如果position为0则插入在链表头，依次类推    // 若position < 0 或者 position > count，则返回underflow    Error_code insert(int position, const List_entry &entry)    {        if (position < 0 ||position > count) return underflow;        if (position==0&&empty())        {            current = new Node<List_entry>(entry,0,0);            curPosition = 0;            count++;            return success;        }        if (position==count)        {            setPosition(count-1);            current->next = new Node<List_entry>(entry,current,0);            current = current->next;            count++;            curPosition++;            return success;        }        setPosition(position);        Node<List_entry> * tmp = new Node<List_entry>(entry,current->back,current);        if (current->back!=0) current->back->next = tmp;//链表插入的重点        current->back = tmp;        current = tmp;        count++;        return success;    }    // 删除第position个位置的元素，并将该元素的值保存在entry中    // 若position < 0 或者 position >= count，则返回underflow    Error_code remove(int position, List_entry &entry)    {        if (position < 0||position >= count) return underflow;        setPosition(position);        Node<List_entry> * tmp = current;        entry = tmp->entry;        if (current->back!=0) //链表删除的重点        {            current->back->next = current->next;            if (current->next!=0) current->next->back = current->back;        }        else            if (current->next!=0) current->next->back = 0;        current = current->next;        count--;        if (count==0)        {            curPosition = -1;            current = 0;        }        delete tmp;        return success;    }    Error_code retrieve(int position, List_entry &entry) const    {        if (position < 0||position >= count) return underflow;        setPosition(position);        entry = current->entry;        return success;    }    // 将第position个位置的元素替换为entry    // 若position < 0 或者 position >= count，则返回underflow    Error_code replace(int position, const List_entry &entry)    {        if (position < 0||position >= count) return underflow;        setPosition(position);        current->entry = entry;        return success;    }    // 用visit函数遍历list内所有的元素    void traverse(void (*visit)(List_entry &))    {        if (empty()) return ;        setPosition(0);        while(curPosition!=count-1)        {            visit(current->entry);            current = current->next;            curPosition++;        }        visit(current->entry);    }protected:    int count;                                  // 记录list内元素数量    mutable int curPosition;                    // current指针的位置编号    mutable Node<List_entry> *current;          // current指针    // 设置current指针的位置，指向第position个位置    void setPosition(int position) const    {        if (empty()) return ;        if(curPosition == position) return ;        if (curPosition>=position)        {            while(curPosition!=position)            {                current = current->back;                curPosition--;            }        }        else        {            while(curPosition!=position)            {                current = current->next;                curPosition++;            }        }    }};