public class FrogThread implements Runnable{

    private FrogAction frogAction;
    private int index;
    private int sum;

    public FrogThread(FrogAction frogAction, int index, int sum) {
        this.frogAction = frogAction;
        this.index = index;
        this.sum = sum;
    }

    @Override
    public void run() {
        try {
            frogAction.next(index, sum);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}


public class FrogAction {

    private short n;
    private short[] comars;
    private TreeSet<Integer> set = new TreeSet<>();

    public FrogAction(short n, short[] comars) {
        this.n = n;
        this.comars = comars;
    }

    public TreeSet<Integer> getSet() {
        return set;
    }

    public void next(int index, int sum) throws InterruptedException {
        if (index == n - 1) {
            sum += comars[index];
            set.add(sum);
        } else if (index < n - 1) {
            sum += comars[index];
            Thread threadLeft = new Thread(new FrogThread(this, index + 2, sum));
            Thread threadRight = new Thread(new FrogThread(this, index + 3, sum));
            threadLeft.start();
            threadRight.start();
            threadLeft.join();
            threadRight.join();
        }
    }
}