class Isogram {
  bool isIsogram(String isogram) {
    final List<String> allAlphabeticChars = [];
    final Set<String> uniqueAlphabeticChars = {};
    isogram = isogram.toLowerCase();
    isogram.split('').forEach((char) {
      if (char == char.toLowerCase() &&
          char.codeUnitAt(0) >= 97 &&
          char.codeUnitAt(0) <= 122) {
        allAlphabeticChars.add(char);
        uniqueAlphabeticChars.add(char);
      }
    });
    return allAlphabeticChars.length == uniqueAlphabeticChars.length;
  }
}