Two ways of doing it.
cabins are built as pairs with the one on the right as you are facing it from the hall having the bed by the balcony and the one on the left having the bed by the bath. cabins alternate bed by bath, bed by balcony, bath, balcony, bath etc..
The first way is to identify a pair which can be done by finding a pair of connecting cabins...those are a pair, then just work your way along the hall until you get to your cabin.
The other way is to fond a cabin that is for more than 2 guests and you know that will always have the bed by the bath so by default you will have the bed by the balcony configuration on either side of it, again, follow the pattern
All cabins with 3 or more guests will have the bed by the bath.
Cabins with 2 guests can have either layout.