TỔNG ĐA THỨC

package JavaCoban;

import java.util.ArrayList;
import java.util.Scanner;
import java.util.StringTokenizer;
class SoHang {
    private int heSo,bac;
    public SoHang(int heSo, int bac) {
        this.heSo = heSo;
        this.bac = bac;
    }

    public int getHeSo() {
        return heSo;
    }

    public int getBac() {
        return bac;
    }
}

public class DaThuc {
    private ArrayList<SoHang> arr = new ArrayList<>();

    public DaThuc() {
    }

    public ArrayList<SoHang> getArr() {
        return arr;
    }

    public void setArr(SoHang x) {
        this.arr.add(x);
    }

    @Override
    public String toString() {
        String s = "";
        for (int i = 0; i < arr.size(); i++) {
            if (i != 0) s += " + ";
            s += String.format(arr.get(i).getHeSo() + "*x^" + arr.get(i).getBac());
        }
        return s;
    }

    public DaThuc(String s) {
        StringTokenizer st = new StringTokenizer(s, " + ");
        while (st.hasMoreTokens()) {
            String i = st.nextToken();
            StringTokenizer st2 = new StringTokenizer(i, "*x^");
            while (st2.hasMoreTokens()) {
                SoHang x = new SoHang(Integer.parseInt(st2.nextToken()), Integer.parseInt(st2.nextToken()));
                arr.add(x);
            }
        }
    }

    public DaThuc cong(DaThuc b) {
        DaThuc c = new DaThuc();
        int i = 0, j = 0;
        while (i < this.getArr().size() && j < b.getArr().size()) {
            SoHang cuai = this.arr.get(i), cuaj = b.getArr().get(j);
            if (cuai.getBac() > cuaj.getBac()) {
                c.setArr(cuai);
                i++;
            } else if (cuai.getBac() == cuaj.getBac()) {
                SoHang x = new SoHang(cuai.getHeSo() + cuaj.getHeSo(), cuai.getBac());
                c.setArr(x);
                i++;
                j++;
            } else {
                c.setArr(cuaj);
                j++;
            }
        }
        while (i < this.getArr().size()) {
            c.setArr(this.arr.get(i));
            i++;
        }
        while (j < b.getArr().size()) {
            c.setArr(b.arr.get(i));
            j++;
        }
        return c;
    }

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int t = Integer.parseInt(sc.nextLine());
        while(t-->0){
            DaThuc p = new DaThuc(sc.nextLine());
            DaThuc q = new DaThuc(sc.nextLine());
            DaThuc r = p.cong(q);
            System.out.println(r);
        }
    }

}