import java.util.ArrayList;

public class AB {

    public ArrayList<Integer> rAccmulate(int count)
    {
        if (count <= 0)
            return new ArrayList<Integer>();
        ArrayList<Integer> alAcc = rAccmulate(count - 1);
        alAcc.add(count);
        return alAcc;
    }

    public ArrayList<Integer> rAccmulateB(int count) {
        ArrayList<Integer> ret = new ArrayList<>(count);
        rAccumulateUtil(count, ret);
        return ret;
    }

    private void rAccumulateUtil(int count, ArrayList<Integer> arrLis) {
        if (count <= 0)
            return;
        arrLis.add(count);
        rAccumulateUtil(count - 1, arrLis);
    }
    
    public static void main(String[] args) {
        System.out.println("AA " + (new AB()).rAccmulate(5)); 
        System.out.println("BB " + (new AB()).rAccmulateB(5)); 

    }
}