2св списки

#include <iostream>
#include <string>
#include <fstream>
using namespace std;

ifstream in("input.txt");
ofstream out("output.txt");

template <class Item> class DoublList {
    struct Node {
        Item data;
        Node* prev;
        Node* next;
        Node(Item x) : data(x), next(0), prev(0) {}
    };
    Node* head;
    Node* tail;
    int size;
    Node* Find(int index) {
        Node* cur = head;
        for (int i = 0; i < index; i++) {
            cur = cur->next;
        }
        return cur;
    }

public:
    DoublList() {
        head = NULL;
        tail = NULL;
    }

    bool empty() {
        return head == 0;
    }
    int GetLength() {
        return size;
    }
    Node Get(int index) {
        Node* r = Find(index);
        Item i = r->data;
        return i;
    }
    void insertAtHead(string value) {
        Node* newNode = new Node();
        newNode->data = value;
        newNode->prev = NULL;
        newNode->next = head;

        if (head != NULL) {
            head->prev = newNode;
        }
        else {
            tail = newNode;
        }

        head = newNode;
        size++;
    }

    void insertAtTail(string value) {
        Node* newNode = new Node(value);

        if (tail != NULL) {
            tail->next = newNode;
        }
        else {
            head = newNode;
        }

        tail = newNode;
        size++;
    }

    void deleteAtHead() {
        if (head != NULL) {
            Node* temp = head;

            if (head == tail) {
                head = NULL;
                tail = NULL;
            }
            else {
                head = head->next;
                head->prev = NULL;
            }

            delete temp;
        }
    }

    void deleteAtTail() {
        if (tail != NULL) {
            Node* temp = tail;

            if (head == tail) {
                head = NULL;
                tail = NULL;
            }
            else {
                tail = tail->prev;
                tail->next = NULL;
            }

            delete temp;
        }
    }

    void printList() {
        Node* current = head;

        while (current != NULL) {
            out << current->data << " ";
            current = current->next;
        }

        cout << endl;
    }
};

int main()
{
    DoublList <string> k, m;
    string value;
    while (in >> value) {
        k.insertAtTail(value);
        if (value.length() == 1) {
            k.insertAtTail(value);
        }
    }
    in.close();

    k.printList();
    return 0;
}
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