Excel 列名和列序号转换

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      #region - 由数字转换为Excel中的列字母 -

      public static int ToIndex(string columnName)
      {
          if (!Regex.IsMatch(columnName.ToUpper(), @"[A-Z]+")) { throw new Exception("invalid parameter"); }

          int index = 0;
          char[] chars = columnName.ToUpper().ToCharArray();
          for (int i = 0; i < chars.Length; i++)
          {
              index += ((int)chars[i] - (int)'A' + 1) * (int)Math.Pow(26, chars.Length - i - 1);
          }
          return index - 1;
      }


      public static string ToName(int index)
      {
          if (index < 0) { throw new Exception("invalid parameter"); }

          List<string> chars = new List<string>();
          do
          {
              if (chars.Count > 0) index--;
              chars.Insert(0, ((char)(index % 26 + (int)'A')).ToString());
              index = (int)((index - index % 26) / 26);
          } while (index > 0);

          return String.Join(string.Empty, chars.ToArray());
      }

      #endregion