if (startIndex == word.Length)
                {
                    result.Add(new string(word));
                    return;
                }
                if (char.IsLetter(word[startIndex]))
                {
                    AlternateCharCases(word.ToArray(), startIndex + 1, result);
                    word[startIndex] = Char.ToUpper(word[startIndex]);
                    AlternateCharCases(word.ToArray(), startIndex + 1, result);
                }
                else
                {
                    AlternateCharCases(word, startIndex + 1, result);