求两个字符串最大的子字符串C#

            string str1 = "中国ab-15";
            string str2 = "中国ab-23";
            byte[] char1 = Encoding.UTF8.GetBytes(str1);
            byte[] char2 = Encoding.UTF8.GetBytes(str2);
            int len1 = char1.Length;
            int len2 = char2.Length;
            string maxchar = "";
            List<byte> temp = new List<byte>();
            int maxl = 0;
            for (int i = 0; i < len1; i++)
                for (int j = 0; j < len2; j++)
                {
                    int pos1 = i;
                    int pos2 = j;
                    int l = 0;
                    temp.Clear();
                    while (char1[pos1] == char2[pos2])
                    {
                        l++;
                        temp.Add(char1[pos1]);
                        if (++pos1 > len1 - 1) break;
                        if (++pos2 > len2 - 1) break;
                    }
                    //System.out.println(""+(++loops)+":"+temp);
                    if (l > maxl)
                    {
                        maxl = l;
                        maxchar =Encoding.UTF8.GetString( temp.ToArray());

                    }
                }
            Console.WriteLine("" + maxl + " " + maxchar);