數據結構基礎(13)

采用鏈式存儲的棧成為鏈式棧(或簡稱鏈棧), 鏈棧的優點是便於多個棧共享存儲空間和提高其效率, 且不存在棧滿上溢的情況(因為鏈棧是靠指針鏈接到一起,只要內存夠大, 則鏈棧理論上可以存儲的元素是沒有上限的);

與順序棧相比, 由於順序棧是采用的數組實現, 因此一旦數組填滿, 則必須重新申請內存, 並將所有元素”搬家”, 而鏈棧則省略了這一”耗時耗力”的工作, 但卻需要付出附加一個指針的代價;

鏈棧通常采用單鏈表實現, 並規定所有的操作都必須實在單鏈表的表頭進行, 而且w我們的鏈棧沒有頭結點, m_top直接指向棧頂元素;

鏈式棧的圖示如下:

鏈棧節點構造:

template 
class ChainNode
{
    template 
    friend ostream &operator<<(ostream &os, const LinkStack &stack);
    friend class LinkStack;
private:
    ChainNode(const Type &_data, ChainNode *_next = NULL)
        :data(_data), next(_next) {}

    Type data;
    ChainNode *next;
};

鏈棧設計:

template 
class LinkStack
{
    template 
    friend ostream &operator<<(ostream &os, const LinkStack &stack);
public:
    LinkStack(): m_top(NULL) {}
    ~LinkStack()
    {
        makeEmpty();
    }
    bool isEmpty() const
    {
        return m_top == NULL;
    }

    void pop() throw(std::out_of_range);
    const Type &top() const throw(std::out_of_range);
    void push(const Type &data);
    void makeEmpty();

private:
    ChainNode *m_top;
};

棧的三大操作:

template 
const Type &LinkStack::top() const
throw (std::out_of_range)
{
    if (isEmpty())
        throw std::out_of_range("stack is empty, can`t get data");

    return m_top->data;
}

template 
void LinkStack::pop()
throw (std::out_of_range)
{
    if (isEmpty())
        throw std::out_of_range("stack is empty, can`t delete");

    ChainNode *deleteNode = m_top;
    m_top = m_top->next;
    delete deleteNode;
}

template 
void LinkStack::push(const Type &data)
{
    //此處是整個鏈棧的關鍵點
    // 該操作會生成一個節點,
    // 並自動將m_top上移一格,
    // 而且將m_top原先指向的節點, 作為新生成的節點的下一節點
    //注意此處
    //如果第一次運行push, 則原m_top為NULL
    // 新m_top指向第一個元素
    m_top = new ChainNode(data, m_top);
}

清空整個棧:

template 
void LinkStack::makeEmpty()
{
    while (!isEmpty())
    {
        pop();
    }
}

輸出棧內所有內容:

template 
ostream &operator<<(ostream &os, const LinkStack &stack)
{
    ChainNode *currentNode = stack.m_top;
    while (currentNode != NULL)
    {
        cout << currentNode->data << ' ';
        currentNode = currentNode->next;
    }

    return os;
}

測試代碼:

int main()
{
    LinkStack test;
    for (int i = 0; i < 10; ++i)
    {
        test.push(rand()%100);
    }

    cout << test << endl;
    cout << "top = " << test.top() << endl;

    test.pop();
    cout << "top = " << test.top() << endl;

    test.push(1);
    cout << "top = " << test.top() << endl;

    while (!test.isEmpty())
    {
        test.pop();
    }
    cout << test << endl;

    test.push(11);
    test.push(22);
    test.push(33);
    cout << test << endl;
    test.makeEmpty();

    try
    {
        cout << "top = " << test.top() << endl;
    }
    catch (const std::exception &e)
    {
        cerr << e.what() << endl;
    }

    return 0;
}