哪位高人能帮我想下这个反向的算法？

Question

现有以下方法 可以根据传进来的字符串 转换编码为正常的中文public static string decode(string str)
        {
            string str2 = "";
            for (int i = 0; i < str.Length; i++)
            {
                int num2 = str[i];
                if ((str[i] != 0xff5e) && (str[i] != 0x9f9f))
                {
                    if (num2 >= 0x4e00)
                    {
                        str2 = str2 + ((char)((str[i] - '\n') + 2));
                    }
                    else
                    {
                        str2 = str2 + str[i];
                    }
                }
                else
                {
                    str2 = str2 + str[i];
                }
            }
            return str2;
        }
把字符串“昷挏枉乂中釕皌妒娨副吘４悫耍号囨醀丵毚、甽觫贰紒乹、”传进方法里，就能返回“孕妇在早孕期间经常出现择食、食欲不振”这个字符串现在我想实现的是  写一个方法 把“孕妇在早孕期间经常出现择食、食欲不振”传进去，返回“昷挏枉乂中釕皌妒娨副吘４悫耍号囨醀丵毚、甽觫贰紒乹、”  相当于把上面的方法的反向运算  请问大家这个方法该如何写？？

Answer 1

        public static string encode(string str)
        {
            string str2 = "";
            for (int i = 0; i < str.Length; i++)
            {
                int num2 = str[i];
                if ((str[i] != 0xff5e) && (str[i] != 0x9f9f))
                {
                    if (num2 >= 0x4e00)
                    {
                        str2 = str2 + ((char)(str[i] +8));
                        int a = str[i];
                        int b = '\n';
                        int c = str2[i];
                    }
                    else
                    {
                        str2 = str2 + str[i];
                    }
                }
                else
                {
                    str2 = str2 + str[i];
                }
            }
            return str2;
        }