[APS] Hidden Numbers

//ako cifrata e pogolema od 4, vnesi nov jazol od brojot koj go gradat so soednata cifra i izbrisi gi starite jazli!
import java.util.NoSuchElementException;
import java.util.Scanner;

public class HiddenNumbers
{
    public static void find_numbers(SLL<Integer> list){
        SLLNode<Integer> curr= list.getFirst();
        SLLNode<Integer> prev= list.getFirst();
        while(curr!=null){
            curr=prev.succ;
            if(curr==null) break;
            if(prev.element>4){
                int number= Integer.parseInt(prev.element+""+curr.element);
                list.insertBefore(number,prev);
                list.delete(prev);
                prev=curr;
                curr=curr.succ;
                list.delete(prev);
                prev=curr;
            }
            else{
                prev=curr;
            }
        }
    }

    public static void main(String[] args)
    {
        Scanner input= new Scanner(System.in);
        int n= Integer.parseInt(input.nextLine());
        SLL<Integer> list= new SLL<Integer>();
        String[] cifra= input.nextLine().split("\\s+");
        for(int i=0;i<n;i++){
            list.insertLast(Integer.parseInt(cifra[i]));
        }
        find_numbers(list);
        System.out.println(list.toString());
    }
}



class SLLNode<E> {
    protected E element;
    protected SLLNode<E> succ;

    public SLLNode(E elem, SLLNode<E> succ) {
        this.element = elem;
        this.succ = succ;
    }

    @Override
    public String toString() {
        return element.toString();
    }
}

class SLL<E> {
    private SLLNode<E> first;

    public SLL() {
        this.first = null;
    }

    public void deleteList() {
        first = null;
    }

    public int length() {
        int ret;
        if (first != null) {
            SLLNode<E> tmp = first;
            ret = 1;
            while (tmp.succ != null) {
                tmp = tmp.succ;
                ret++;
            }
            return ret;
        } else
            return 0;

    }

    @Override
    public String toString() {
        String ret = new String();
        if (first != null) {
            SLLNode<E> tmp = first;
            ret += tmp;
            while (tmp.succ != null) {
                tmp = tmp.succ;
                ret += " " + tmp;
            }
        } else
            ret = "Prazna lista!!!";
        return ret;
    }

    public void insertFirst(E o) {
        SLLNode<E> ins = new SLLNode<E>(o, first);
        first = ins;
    }

    public void insertAfter(E o, SLLNode<E> node) {
        if (node != null) {
            SLLNode<E> ins = new SLLNode<E>(o, node.succ);
            node.succ = ins;
        } else {
            System.out.println("Dadenot jazol e null");
        }
    }

    public void insertBefore(E o, SLLNode<E> before) {
        if (first != null) {
            SLLNode<E> tmp = first;
            if (first == before) {
                this.insertFirst(o);
                return;
            }
            while (tmp.succ != before)
                tmp = tmp.succ;
            if (tmp.succ == before) {
                SLLNode<E> ins = new SLLNode<E>(o, before);
                tmp.succ = ins;
            } else {
                System.out.println("Elementot ne postoi vo listata");
            }
        } else {
            System.out.println("Listata e prazna");
        }
    }

    public void insertLast(E o) {
        if (first != null) {
            SLLNode<E> tmp = first;
            while (tmp.succ != null)
                tmp = tmp.succ;
            SLLNode<E> ins = new SLLNode<E>(o, null);
            tmp.succ = ins;
        } else {
            insertFirst(o);
        }
    }

    public E deleteFirst() {
        if (first != null) {
            SLLNode<E> tmp = first;
            first = first.succ;
            return tmp.element;
        } else {
            System.out.println("Listata e prazna");
            return null;
        }
    }

    public E delete(SLLNode<E> node) {
        if (first != null) {
            SLLNode<E> tmp = first;
            if (first == node) {
                return this.deleteFirst();
            }
            while (tmp.succ != node && tmp.succ.succ != null)
                tmp = tmp.succ;
            if (tmp.succ == node) {
                tmp.succ = tmp.succ.succ;
                return node.element;
            } else {
                System.out.println("Elementot ne postoi vo listata");
                return null;
            }
        } else {
            System.out.println("Listata e prazna");
            return null;
        }
    }

    public SLLNode<E> getFirst() {
        return first;
    }

    public SLLNode<E> find(E o) {
        if (first != null) {
            SLLNode<E> tmp = first;
            while (tmp.element != o && tmp.succ != null)
                tmp = tmp.succ;
            if (tmp.element == o) {
                return tmp;
            } else {
                System.out.println("Elementot ne postoi vo listata");
            }
        } else {
            System.out.println("Listata e prazna");
        }
        return first;
    }
}
/*
5
6 4 4 4 6
64 4 4 6

6
3 3 6 9 2 6
3 3 69 2 6

7
1 7 2 7 7 5 3
1 72 77 53
 */