PV913ListClass

#include <iostream>

template <typename ElemT>
class List
{
    class Node
    {
    public:
        ElemT data;
        Node* next;
        Node* prev;
        Node(const ElemT& dataP, Node* nextP = nullptr, Node* prevP = nullptr)
            :data{ dataP }, next{ nextP }, prev{prevP} {};
    };

    Node* head;
    Node* tail;
    size_t size;
    Node* getNode(size_t idx);
public:
    List() : head{ nullptr }, tail{ nullptr }, size{ 0 } {}
    ElemT& front() { return head->data; };
    const ElemT& front()const { return head->data; };
    ElemT& back() { return tail->data; };
    const ElemT& back()const { return tail->data; };
    const size_t getSize() const { return size; };
    bool empty() const { return size == 0; };
    void push_back(const ElemT& data);
    void push_front(const ElemT& data);
    bool pop_back();
    bool pop_front();
    void clear();
    ElemT& operator[](size_t idx);
    void insertAt(size_t idx, const ElemT& data);
    void deleteAt(size_t idx);
    ~List();
};

template <typename ElemT>
void List<ElemT>::push_back(const ElemT& data)
{
    Node* tmp{ tail };
    tail = new Node{ data, nullptr, tail };
    if (tmp)
    {
        tmp->next = tail;
    }
    ++size;

    if (!head)
    {
        head = tail;
    }
    //if (!head)
    //{
    //  head = new Node{ data };
    //  tail = head;
    //}
    //else
    //{
    //  tail->next = new Node{ data, nullptr, tail };
    //  tail = tail->next;
    //}
    //++size;
}

template <typename ElemT>
void List<ElemT>::push_front(const ElemT& data)
{
    Node* tmp{ head };
    head = new Node{ data, head, nullptr };
    if (tmp)
    {
        tmp->prev = head;
    }
    ++size;

    if (!tail)
    {
        tail = head;
    }
}

template <typename ElemT>
bool List<ElemT>::pop_front()
{
    if (head)
    {
        if (tail == head)
        {
            delete tail;
            size = 0;
            tail = nullptr;
            head = nullptr;
            return true;
        }

        Node* tmp{ head };
        head = head->next;
        head->prev = nullptr;
        delete tmp;
        --size;
        return true;
    }
    return false;
}
template <typename ElemT>
bool List<ElemT>::pop_back()
{
    if (tail)
    {
        if (tail == head)
        {
            delete tail;
            size = 0;
            tail = nullptr;
            head = nullptr;
            return true;
        }

        Node* tmp{ tail };
        tail = tail->prev;
        tail->next = nullptr;
        delete tmp;
        --size;
        return true;
    }
    return false;
}

template <typename ElemT>
void List<ElemT>::clear()
{
    while (tail)
    {
        std::cout << "Clear for: " << back() << '\n';
        pop_back();
    }
}

template <typename ElemT>
List<ElemT>::~List()
{
    while (head)
    {
        std::cout << "Destruct for: " << front() << '\n';
        pop_front();
    }
}

template<typename ElemT>
typename List<ElemT>::Node* List<ElemT>::getNode(size_t idx)
{
    Node* curr{ nullptr };
    int cnt;

    if (idx >= 0 and idx < size)
    {
        if (idx > (size / 2))
        {
            for (curr = tail, cnt = size - 1; cnt > idx; curr = curr->prev, --cnt);
        }
        else
        {
            for (curr = head, cnt = 0; cnt < idx; curr = curr->next, ++cnt);
        }
    }
    return curr;
}

template <typename ElemT>
ElemT& List<ElemT>::operator [](size_t idx)
{
    return getNode(idx)->data;
};

template<typename ElemT>
void List<ElemT>::insertAt(size_t idx, const ElemT& data)
{
    Node* curr = getNode(idx);
    if (!curr or curr == tail) { push_back(data); return; };

    Node* newNode = new Node{ data, curr->next, curr };
    curr->next = newNode;
    newNode->next->prev = newNode;
    ++size;
}

template<typename ElemT>
void List<ElemT>::deleteAt(size_t idx)
{
    Node* curr = getNode(idx);
    if (curr)
    {
        if (curr->prev) { curr->prev->next = curr->next; }
        else { head = curr->next; }
        if (curr->next) { curr->next->prev = curr->prev; }
        else { tail = curr->prev; }

        --size;

        if (curr == head and curr == tail)
        {
            head = nullptr;
            tail = nullptr;
            size = 0;
        }

        delete curr;
    }

}

int main()
{
    {
        List<int> l;
        l.push_back(1);
        l.push_front(2);
        l.pop_front();
        l.pop_back();
        std::cout << "Size: " << l.getSize() << '\n';
    }

    {
        List<int> l;
        l.push_front(2);
        l.push_back(1);
        l.pop_back();
        l.pop_front();
        std::cout << "Size: " << l.getSize() << '\n';
    }

    {
        List<int> l;
        //l.insertAt(5, 33);
        l.deleteAt(5);
        //std::cout << "Front: " << l.front() << '\n';
        //std::cout << "Back: " << l.back() << '\n';
        std::cout << "Size: " << l.getSize() << '\n';
    }
    List<int> l;

    std::cout << "Size: " << l.getSize() << '\n';
    l.push_back(26);
    l.push_back(42);
    std::cout << "Size: " << l.getSize() << '\n';
    std::cout << "Front: " << l.front() << '\n';
    l.pop_front();
    std::cout << "Front: " << l.front() << '\n';
    l.pop_front();

    l.push_back(1);
    l.push_back(2);
    l.push_back(3);
    l.push_back(4);

    std::cout << "####" << '\n';
    std::cout << "Front: " << l.front() << '\n';
    std::cout << "Back: " << l.back() << '\n';
    std::cout << "####" << '\n';

    l.clear();

    std::cout << "Size: " << l.getSize() << '\n';

    l.push_back(1);
    l.push_back(2);
    l.push_back(3);
    l.push_back(4);
    std::cout << "####" << '\n';
    std::cout << "Front: " << l.front() << '\n';
    std::cout << "Back: " << l.back() << '\n';
    l.pop_back();
    std::cout << "Back: " << l.back() << '\n';
    std::cout << "####" << '\n';

    l.clear();
    std::cout << "Size: " << l.getSize() << '\n';

    l.push_front(22);
    l.push_front(23);
    l.push_front(24);
    std::cout << "####" << '\n';
    std::cout << "Front: " << l.front() << '\n';
    std::cout << "Back: " << l.back() << '\n';

    l.clear();

    for (int i{ 0 }; i < 10; ++i)
    {
        l.push_front(i);
    }
    std::cout << "Size: " << l.getSize() << '\n';
    std::cout << "[][][][][][]\n";
    for (int i{ 0 }; i < l.getSize(); ++i)
    {
        std::cout << l[i] << '\n';
    }
    std::cout << "[][][][][][]\n";

    l.clear();


    l.push_back(333);
    std::cout << "Front: " << l.front() << '\n';
    l.deleteAt(0);

    l.push_front(444);
    std::cout << "Back: " << l.back() << '\n';
    l.deleteAt(0);


    for (int i{ 0 }; i < 10; ++i)
    {
        l.push_front(i);
    }

    l.deleteAt(9);
    l.deleteAt(5);
    l.deleteAt(0);

    std::cout << "Size: " << l.getSize() << '\n';
    std::cout << "[][][][][][]\n";
    for (int i{ 0 }; i < l.getSize(); ++i)
    {
        std::cout << l[i] << '\n';
    }
    std::cout << "[][][][][][]\n";

    l.clear();

    l.insertAt(0, 1);
    l.insertAt(0, 2);
    l.insertAt(0, 3);
    l.insertAt(0, 4);
    l.insertAt(0, 5);
    std::cout << "======\n";
    for (int i{ 0 }; i < l.getSize(); ++i)
    {
        std::cout << l[i] << '\n';
    }
    std::cout << "======\n";
    l.insertAt(2, 333);
    l.deleteAt(3);
    l.insertAt(4, 444);
    std::cout << "Front: " << l.front() << '\n';
    std::cout << "Back: " << l.back() << '\n';

    return 0;
}