ListaUporzadkowana

package listod;

public class ListoD {

    private ListElem first;
    private ListElem last;

    public ListoD() {
        first = null;
        last = null;
    }

    public boolean isEmpty() {
        return (first == null);
    }

    public void print() {
        ListElem current = first;

        while (current != null) {
            System.out.print(current + " ");
            current = current.next;
        }
        System.out.println("");
    }

    public void insert(int value) {
        ListElem newElem = new ListElem(value); //tworzymy nowy element listy

        //lista jest pusta
        if (isEmpty()) {
            first = newElem;
            last = newElem;
        } else { //lista ma co najmniej jeden element
            ListElem current = first; //aktualny element

            while (current != null) {
                if (value < current.data) {
                    break;
                }
                current = current.next;
            }

            //po wyjsciu z petli w miejsce current musimy wstawic nowy element
            if(current == null) { //tzn ze bedziemy wstawiac element na koncu listy
                last.next = newElem;
                newElem.previous = last;
                last = newElem;
            } else if(current.previous == null) { //tzn ze bedziemy wstawiac element na poczatku listy
                first.previous = newElem;
                newElem.next = first;
                first = newElem;
            } else {
                //ani pierwszy ani ostatni
                newElem.next = current;
                newElem.previous = current.previous;
                current.previous.next = newElem;
                current.previous = newElem;
            }
        }
    }

    public ListElem deleteFirst() {
        if (isEmpty()) {
            return null;
        }
        ListElem temp = first;
        if (first.next == null) {
            last = null;
        } else {
            first.next.previous = null;
        }
        first = first.next;
        return temp;
    }

    public ListElem deleteLast() {
        if (isEmpty()) {
            return null;
        }
        ListElem temp = last;
        if (first.next == null) {
            first = null;
        } else {
            last.previous.next = null;
        }
        last = last.previous;
        return temp;
    }

    public ListElem find(int value){
        if(isEmpty()) return null;
        ListElem current = first;

        while(current != null) {
            if(current.data == value){
                return current;
            }
            current = current.next;
        }
        return null;
    }

    public ListElem finds(int elem)     // Wyszukiwanie elementu
    {
        if (isEmpty()) return null;

        ListElem current = first;  // Rozpoczynamy od pierwszego elementu
        while (current.data != elem)
        {
            if (current.next == null) return null;
            else
                current = current.next;
        }
        return current;
    }

    public static void main(String[] args) {
        ListoD theList = new ListoD();

        theList.insert(22);       // wstawiamy na początek
        theList.insert(44);
        theList.insert(33);
        theList.print();         // wypisujemy zawartość listy

        theList.insert(11);        // wstawiamy na koniec
        theList.insert(33);
        theList.insert(55);
        theList.insert(2);
        theList.insert(100);
        theList.insert(99);
        theList.insert(3);
        theList.insert(1);
        theList.insert(1);
        theList.insert(1);
        theList.insert(1000);
        theList.insert(1000);
        theList.insert(1000);

        theList.print();         // wypisujemy zawartość listy

        theList.deleteFirst();         // usuwamy pierwsze dwa elementy
        theList.deleteFirst();

        theList.print();         // wypisujemy ponownie

        theList.deleteLast(); //usuwamy ostatni element

        theList.print();         // wypisujemy ponownie

        System.out.println(theList.find(-9));
        System.out.println(theList.find(22));
    }

}