using System;

using System.Text;

public class Program

{

    public static void Main()

    {

        string[] datas = { "ASDGE", "ADQWDESDASD", "ADQWDESDASDWTEGRET", "ADQWDESDASDWTEGRETQWERTYU" };

        foreach(var data in datas)

        {

            StringBuilder sb = new StringBuilder(data);

            string result = string.Empty;

​

            /* 2019-09-25 隱碼規則:

             * 小於四位不隱碼

             * 姓名1~7位=>隱3碼

             * 姓名8~14位=>隱4碼

             * 姓名15~22=>隱6碼

             * 姓名22以上=>隱10碼

             * 以上規則都從前面數起第三位開始隱碼

             */

            if (data.Length < 4)

            {

                result = data;

            }

            else

            {

                // 計算隱碼數量

                int amountOfMark = (data.Length <= 7) ? 3 : (data.Length >= 8 && data.Length <= 14) ? 4 : (data.Length >= 15 && data.Length <= 22) ? 6 : 10;

                // 開始隱碼的位置

                int startIndex = 2;

                result = sb.Remove(startIndex, amountOfMark).Insert(startIndex, new string('*', amountOfMark)).ToString();

                // 驗算

                Console.WriteLine("string length : " + data.Length + ", mark length : " + amountOfMark + ", result : " + result);

            }           

        }       

    }

}