[H0riz0n]

Both are correct
The contracted form of the helping verbs : isn't , wasn't , hasn't , haven't , hadn't, don't, ...etc is a single word and must precede the subject in the interrogative form

While is not , was not , has not , have not, had not, do not, ....etc. are two seperate words. Each pair of words is formed of : positive helping verb + not "an adverb to form a negative phrase)
You are only allowed to take the helping verb before the subject and leave the adverb "not" in its place

This also occurs in the fomation of the question tag

She has posted all the letters, hasn't she?
She has posted all the letters, has she not?
The second sentence is grammatically correct, however it is rare to use as the question tag is a spoken form and contracted forms are preferred in spoken English