It would help, in future, if you were to tell us what an "isogram" is; just in case we haven't seen this word since we were in school doing the same assignment you might be doing.

According to a quick websearch:

An isogram is a text that does not repeat a letter.

It seems to me that all you need to do is to break your text up into letters and then check if they are all unique. You could do this latter part by sorting them and then walking the length of the sorted text testing to see if the current letter is the same as the previous; or you could take advantage of the fact that hash keys must be unique...

The second option is faster, but both will be correct. Which ever way you choose, have a go at it and come back if you have any problems.

all the best,