[Java][АПС] - Најди го бројот (со Стек)

import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.Scanner;

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

	public SLL() {
		// Construct an empty 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;
			}
			//ako first!=before
			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;
	}

    public Iterator<E> iterator () {
    // Return an iterator that visits all elements of this list, in left-to-right order.
        return new LRIterator<E>();
    }

	// //////////Inner class ////////////

	private class LRIterator<E> implements Iterator<E> {

		private SLLNode<E> place, curr;

		private LRIterator() {
			place = (SLLNode<E>) first;
			curr = null;
		}

		public boolean hasNext() {
			return (place != null);
		}

		public E next() {
			if (place == null)
				throw new NoSuchElementException();
			E nextElem = place.element;
			curr = place;
			place = place.succ;
			return nextElem;
		}

		public void remove() {
			//Not implemented
		}
	}

	public void mirror(){
		if (first != null) {
			//m=nextsucc, p=tmp,q=next
			SLLNode<E> tmp = first;
			SLLNode<E> newsucc = null;
			SLLNode<E> next;

			while(tmp != null){
				next = tmp.succ;
				tmp.succ = newsucc;
				newsucc = tmp;
				tmp = next;
			}
			first = newsucc;
		}

	}

	public void merge (SLL<E> in){
		if (first != null) {
			SLLNode<E> tmp = first;
			while(tmp.succ != null)
				tmp = tmp.succ;
			tmp.succ = in.getFirst();
		}
		else{
			first = in.getFirst();
		}
	}
}
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();
	}
}

public class FormingDigits {
	public static SLL<Integer> function(SLL<Integer> lista){
		SLLNode<Integer> tmp = lista.getFirst();
		SLLNode<Integer> tmp2 = null;
		String str = "";
		int counter = 0,flag = 0;
		while(tmp!=null) {
			tmp2 = tmp;
			while(tmp2.element!=-1) {
				++counter;
				str+=tmp2.element.toString();
				tmp2 = tmp2.succ;
				if(tmp2==null)
				{
					while(tmp.succ!=tmp2) {
						SLLNode<Integer> help = tmp;
						lista.delete(help);
						tmp = tmp.succ;
					}
					lista.insertBefore(Integer.parseInt(str),tmp);
					lista.delete(tmp);
					flag = 1;
					break;
				}
			}
			if(flag==0&&tmp2!=tmp) {
				lista.insertBefore(Integer.parseInt(str), tmp);
				SLLNode<Integer> smena = tmp;
				tmp = tmp2;
				tmp2 = smena;
				while(tmp2!=tmp) {
					smena = tmp2;
					lista.delete(smena);
					tmp2 = tmp2.succ;
				}
				str = "";
			}
			tmp = tmp.succ;
		}

		return lista;
	}
	public static void main(String[] args) {
		Scanner input = new Scanner(System.in);
		int n = input.nextInt();

		SLL<Integer> lista = new SLL<Integer>();
		for(int i=0;i<n;i++) {
			lista.insertLast(input.nextInt());
		}
		System.out.println(function(lista));


	}

}