I need a structure <K, V> where I can easily retrieve either the V given K as usually and viceversa. I used a

MutableMap

till now, but it's quite ugly to extract the K given the V (I can loop on the whole

entries

and get the first match). Is there anything better for my case?

MutableMaps use hashes of keys to retrieve values in

O(1)

, retrieving keys by value is slower as it needs to search through all keys to get one with a matching value. A list of pairs could do the job, but that would be O(n) both ways

Two maps is the easiest way.

it's called BiMap and used to be part of Guava. I'd check the implementation. https://github.com/google/guava/wiki/NewCollectionTypesExplained#bimap

nice idea