My solution, seems to be working fine

[David_Medeiros]

bool FBullCowGame::IsIsogram(FString Word) const
{
	// treat 0 and 1 letter words as isograms
	if (Word.length() <= 1) { return true; }

	TMap<char, bool> LetterSeen; // setup our map
	for (auto Letter : Word)
	{
		Letter = tolower(Letter); // handle mixed case
		if (LetterSeen[Letter])
		{
			return false;
		}
		else
		{
			LetterSeen[Letter] = true;
		}
	}
	return true; // for example in cases where /0 is entered
}