"Jumping out through a closed window is not a good idea."
Translation:Att hoppa ut genom ett stängt fönster är ingen bra idé.
We usually say that inte and not negate verbs, while ingen/inget/inga and no negate nouns.
In a case like this, it's a little unclear what is negated.
It's quite possible to use inte in this sentence, especially if it's clearly the verb that is negated (it's an accepted answer too). For instance, John kept telling me that jumping out the window is a good idea, but it really isn't.
You can compare to how in English, you can say either It's no big deal or It's not a big deal.
I am also wondering what other cases exist like this where "not a" becomes "ingen" instead of "inte en." Dutch uses this wording a lot ("het is geen beer" => "it is no bear" instead of "it is not a bear"), but haven't seen Swedish use the construction in any other instances. Would appreciate a native explaining why it is so in this sentence. :)