循环双向链表复制构造函数 C++

Question

我正在尝试将复制构造函数实现到我的循环双向链表中，但我无法使其工作。文件确实复制了，但顺序不正确。（注意：plate 定义为 template<typename T>，我会尽量只包括相关功能）

Class:

plate class CircularDoubleDirectedList : public ICircularDoubleDirectedList<T> {
private:
    plate class Node {
    public:
        T data;
        Node *next;
        Node *prev;
    };
    Node<T> *current;
    int nrOfElements;
    direction currentDirection;
public:
    CircularDoubleDirectedList() { nrOfElements = 0; currentDirection = FORWARD; current = nullptr; }
    virtual ~CircularDoubleDirectedList();
    CircularDoubleDirectedList(const CircularDoubleDirectedList<T>& origObj);
    CircularDoubleDirectedList& operator=(const CircularDoubleDirectedList<T>& origObj);
    void addAtCurrent(const T& element);
    T getElementAtCurrent() const;
    void removeAtCurrent();
    int size() const;
    void changeDirection();
    void moveCurrent();
    direction getCurrentDirection() const;
};

我对复制构造函数的尝试：

plate CircularDoubleDirectedList<T>::CircularDoubleDirectedList(const CircularDoubleDirectedList<T>& origObj) {
    current = nullptr;
    nrOfElements = 0;
    Node<T> *tmp = origObj.current;
    currentDirection = origObj.currentDirection;

    while (nrOfElements < origObj.nrOfElements) {
        addAtCurrent(tmp->data);
        tmp = tmp->next;
    }
}

加法器：

plate void CircularDoubleDirectedList<T>::addAtCurrent(const T& element) {
    Node<T> *tmp = new Node<T>;
    tmp->data = element;
    tmp->next = nullptr;
    tmp->prev = nullptr;

    if (current == nullptr) {
        tmp->next = tmp;
        tmp->prev = tmp;
        }

    else if (nrOfElements == 1) {
        tmp->next = current;
        tmp->prev = current;
        current->next = tmp;
        current->prev = tmp;
    }

    else {

        if (currentDirection == FORWARD) {
            tmp->prev = current;
            tmp->next = current->next;
            current->next->prev = tmp;
            current->next = tmp;
        }

        else if (currentDirection == BACKWARD) {
            tmp->prev = current->prev;
            tmp->next = current;
            current->prev->next = tmp->prev;
            current->prev = tmp;
        }
    }

    nrOfElements += 1;
    current = tmp;
}

谢谢。

Answer 1

正如我在评论中指出的那样，问题似乎出在最后一个函数中。所以我尝试以一种更具可读性的方式从头开始编写它：

plate void CircularDoubleDirectedList<T>::addAtCurrent(const T& element) {
    Node<T> *tmp = new Node<T>;
    tmp->data = element;

    if (current == nullptr) {
        tmp->next = tmp;
        tmp->prev = tmp;
    } else {
        Node<T> * before, after;
        if (currentDirection == FORWARD) {
            before = current;
            after = current->next;
        } else {  // BACKWARD
            before = current->prev;
            after = current;
        }

        before->next = tmp;
        tmp->prev = before;
        after->prev = tmp;
        tmp->next = after;
    }

    nrOfElements += 1;
    current = tmp;
}

我在复制构造函数中看到另一个问题：如果 currentDirection 是向后的，您正在从左到右读取元素，但以 "afterward" 的方式添加元素，结果顺序丢失。有两种解决方法：可以在扫描时尊重顺序，或者将currentDirection设置为FORWARD，然后设置为正确的值。

plate CircularDoubleDirectedList<T>::CircularDoubleDirectedList(const CircularDoubleDirectedList<T>& origObj) {
    current = nullptr;
    nrOfElements = 0;
    currentDirection = FORWARD;  // set the scan direction temporarily

    for (Node<T> *tmp = origObj.current; nrOfElements < origObj.nrOfElements; tmp = tmp->next) {
        addAtCurrent(tmp->data);
    }
    if (nrOfElements > 0)
        current = current->next;  // align with the current of the copyed list
    currentDirection = origObj.currentDirection;  // set the right direction
}

如果解决了您的问题，请告诉我。

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