"An armchair in a bedroom."
Translation:Крісло у спальні.
They have the same meaning, it's about euphony :)
Ukrainian tries to avoid congestion of consonants. If you put "в" in this sentence, you will have sequence of 3 consonants (в, с, п) which is not good.
So the general rule (when choosing в over у or і over й) is that you have to try to have as little consonants in a row as possible.