算法

            string[] b = new string[] { "1", "3", "4", "5", "6", "7", "8", "9"};
            string[] a = new string[] { "2", "3", "4", "5", "6", "9" };
            StringBuilder sb = new StringBuilder(); 

 

            int i = 0;

            for (int j =0; j < a.Length; j++)
            {
                for (int m = i; m < b.Length; m++)
                {
                    if (a[j] == b[m])
                    {
                        sb.Append(b[m]);
                        i = m;
                        break;
                    }
                }
            }