#include<iostream>

using namespace std;

class List {
    struct Elem {
        int data_;
        Elem* next_;
        Elem* prev_;

        Elem(int val)
        : data_(val),
          next_(0),
          prev_(0)
        {}
    };
    Elem* head_;
    Elem* tail_;

    int size_;

public:
    	List()
	: head_(0),
	  tail_(0),
	  size_(0){}

    //~List();


	void push_back(const int& value){

		    Elem *element = new Elem(value);

		    if (head_ == NULL) {
			head_ = element;
		    } else {
			Elem *last = head_;
			while (last->next_ != NULL)
			    last = last->next_;
			    last->next_ = element;
			    element->prev_ = last;
			    tail_ = element;
		    }

		size_++;
	}


	void pop_back(){

		if (head_ == NULL) {
			cout << "Cannot delete from empty list" << endl;
		} else {
			delete tail_;
			tail_ = tail_->prev_;
			tail_->next_ = NULL;
			size_--;
		}

	}


	void push_front(const int& value){

		    Elem *element = new Elem(value);

		    if (head_ == NULL) {
			head_ = element;
		    } else {
			element->next_ = head_;
			head_->prev_ = element;
			head_ = element;
		    }
		size_++;
	}


	void pop_front(){

		if (head_ == NULL) {
			cout << "Cannot delete from empty list" << endl;
		} else {
			delete head_;
			head_ = head_->next_;
			head_->prev_ = NULL;
			size_--;
		}
	}



	int& front(){
		return head_->data_;
	}


	const int& front() const{
		return head_->data_;
	}


	int& back(){
		return tail_->data_;
	}

	const int& back() const{
		return tail_->data_;
	}

	int size() const{

		if(size_){
			return size_;
		}
	}

	bool empty() const{
		if(head_){
			return false;
		}else{
			return true;
		}
	}


	void clear(){
		if(head_){
			while(head_->next_ != NULL){
				pop_front();
			}

			delete head_;
			head_ = NULL;
			size_ = 0;
		}else{
			cout << "No elemets in the list" << endl;
		}
	}


	void swap(List& other){

		Elem *temp;

		temp = other.head_;
		other.head_ = head_;
		head_ = temp;


	}

	//into proccess
	List(const List& other){


	}

	List& operator=(const List& other){

		//clear();
		head_ = other.head_;
		size_ = other.size_;
	}
	void print(){

		if(head_){
			cout << head_->data_ << endl;
			while(head_->next_ != NULL){
				head_ = head_->next_;
				cout << head_->data_ << endl;
			}
		}else{
			cout << "No elemets in the list" << endl;
		}
	}
};

int main(){

	List list;

	list.push_back(5);
	list.push_back(10);
	list.push_back(15);

	List list2;
	//List list2(list);
	/*list2.push_back(69);
	list2.push_back(73);
	list2.push_back(58);
	list2.push_back(77);*/

	//list.swap(list2);
	list2 = list;
	list2.print();
	//list2.print();
	//list.push_front(69);
	//list.pop_back();
	//list.pop_front();

	//list.front() = 67;
	//list.back() = 99;
	//list.print();
	//list.clear();
	//list.print();

	//cout << list.size() << endl;
	//cout << list.empty() << endl;

	return 0;
}