[APS] Споредби без граници

//juni 2020 - termin 1
//se sporeduvaat element od napred i od pozadi vo parovi po oddalecenost do sredina, taka sto se dodava nivniot zbir na pocetok, pa se dodava pogolemiot od dvata broja do nego i potoa se brisi prviot broj. Nez poubo da objasnam razgledaj spored test cases auf
import java.util.Scanner;
class DLLNode<E> {
    protected E element;
    protected DLLNode<E> pred, succ;

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

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

class DLL<E> {
    private DLLNode<E> first, last;

    public DLL() {
        // Construct an empty SLL
        this.first = null;
        this.last = null;
    }

    public void deleteList() {
        first = null;
        last = null;
    }

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

    }

    public DLLNode<E> find(E o) {
        if (first != null) {
            DLLNode<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 void insertFirst(E o) {
        DLLNode<E> ins = new DLLNode<E>(o, null, first);
        if (first == null)
            last = ins;
        else
            first.pred = ins;
        first = ins;
    }

    public void insertLast(E o) {
        if (first == null)
            insertFirst(o);
        else {
            DLLNode<E> ins = new DLLNode<E>(o, last, null);
            last.succ = ins;
            last = ins;
        }
    }

    public void insertAfter(E o, DLLNode<E> after) {
        if(after==last){
            insertLast(o);
            return;
        }
        DLLNode<E> ins = new DLLNode<E>(o, after, after.succ);
        after.succ.pred = ins;
        after.succ = ins;
    }

    public void insertBefore(E o, DLLNode<E> before) {
        if(before == first){
            insertFirst(o);
            return;
        }
        DLLNode<E> ins = new DLLNode<E>(o, before.pred, before);
        before.pred.succ = ins;
        before.pred = ins;
    }

    public E deleteFirst() {
        if (first != null) {
            DLLNode<E> tmp = first;
            first = first.succ;
            if (first != null) first.pred = null;
            if (first == null)
                last = null;
            return tmp.element;
        } else
            return null;
    }

    public E deleteLast() {
        if (first != null) {
            if (first.succ == null)
                return deleteFirst();
            else {
                DLLNode<E> tmp = last;
                last = last.pred;
                last.succ = null;
                return tmp.element;
            }
        }
        // else throw Exception
        return null;
    }

    public E delete(DLLNode<E> node) {
        if(node==first){
            deleteFirst();
            return node.element;
        }
        if(node==last){
            deleteLast();
            return node.element;
        }
        node.pred.succ = node.succ;
        node.succ.pred = node.pred;
        return node.element;

    }

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

    public String toStringR() {
        String ret = new String();
        if (last != null) {
            DLLNode<E> tmp = last;
            ret += tmp + "<->";
            while (tmp.pred != null) {
                tmp = tmp.pred;
                ret += tmp + "<->";
            }
        } else
            ret = "Prazna lista!!!";
        return ret;
    }

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

    public DLLNode<E> getLast() {

        return last;
    }

    public void izvadiDupliIPrebroj(){

    }
}
public class KashaPopara {
    public static void funkcija(DLL<Integer> list){
        DLLNode<Integer> front= list.getFirst();
        DLLNode<Integer> rear= list.getLast();
        DLLNode<Integer> prev= list.getFirst();
        int sum=0;
        while(front!=rear){
            //System.out.println(list);
            prev=front;
            sum= front.element+rear.element;
            list.insertBefore(sum,front);
            if(front.element> rear.element){
                list.insertBefore(front.element,front);
            }
            else{
                list.insertBefore(rear.element,front);
            }
            prev=prev.pred;
            //System.out.println(list);
            list.delete(front);
            front=prev.succ;
            if(rear==null) break;
            rear=rear.pred;
            //System.out.println(front+" "+rear);
            if(front==rear.pred){
                sum= front.element+rear.element;
                list.insertBefore(sum,front);
                if(front.element> rear.element){
                    list.insertBefore(front.element,front);
                }
                else{
                    list.insertBefore(rear.element,front);
                }
                list.delete(front);
                break;
            }
        }
    }
    public static void main(String[] args) {
        Scanner input= new Scanner(System.in);
        int n= Integer.parseInt(input.nextLine());
        String[] broevi= input.nextLine().split("\\s+");
        DLL<Integer> lista= new DLL<>();
        for(int i=0;i<n;i++){
            lista.insertLast(Integer.parseInt(broevi[i]));
        }
        funkcija(lista);
        System.out.println(lista);
    }
}
/*
6
1 5 7 12 2 6
7<->6<->7<->5<->19<->12<->12<->2<->6

5
10 4 5 3 6
16<->10<->7<->4<->5<->3<->6
*/