public static void Bai230()

        {

            Console.WriteLine(" Mang A:")

            //int[] A = TaoMangNgauNhien();

            clsXulyMang.XuatMang(A);

        int dem = 1;

            for (int i = 0; i < A.Length; i++)

            {

                for (int j=i+1; j<A.Length; j++)

                {

                    if (A[j] == A[i])

                    {

                        dem += 1;       

                    }

                    Console.WriteLine($"{A[i]} xuat hien {dem} lan  ");

                    dem = 1;

                }

            }