The Swedish and English versions don't match up, and it's sometimes difficult to know when one should give a literal translation and when one should provide a more "natural" sounding one.
In this case, if the "correct" answer is to not be a literal translation then the current "correct" doesn't sound very natural. "I had not thought of that" is probably more how I would say it, or "I had not given it a/any thought".
I generally agree, but "I had not thought of that" translates much better into Swedish as Jag hade inte tänkt på det, or more often in the past tense: Jag tänkte inte på det. That sentence actually also features in the course.
I'm actually unclear on the usage of this sentence. Is the meaning:
- I hadn't thought of that (used in a situation where someone present an new idea which you hadn't considered)
- I thought no such thing/I wouldn't think of it (used in a situation where you want to make it clear that you did not have a particular thought and as such had no intention of doing something.)
- Joe: Hey Bob, if your internet isn't working, try restarting your modem.
Bob: Oh ya! I hadn't thought of that!
Joe: I saw you looking at my cookie. You were thinking of eating it!
- Bob: No! I thought no such thing!
The second alternative is the right usage. As I as a Swede ge the context
Odd that "I had not a thought of that" was not accepted, whilst I was offered instead "I had not 1 thought of that."
The "convert one to 1" feature truly is baffling at times. I've added "a" as an alternative now.
- I hadn't thought (of) that = Jag hade inte tänkt (på) det
- I had no thought of that = Jag hade inte en tanke på det
I mean, they're obviously close but they're not quite the same thing. :)
It's just not idiomatic Swedish, but we accept both "not a" and "no" when translating to English. Someone has turned off the "translate into Swedish" option for this exercise - I suspect it's for this very reason. It's a very good phrase to know, so I don't want to remove it entirely, but it's certainly not easy to teach well on Duolingo.