Bidirectional multimap equivalent data structure

Question

I know that Guava has a BiMultimap class internally but didn't outsource the code. I need a data structure which is bi-directional, i.e. lookup by key and by value and also accepts duplicates.

i.e. something like this: (in my case, values are unique, but two values can point to the same key)

0 <-> 5
1 <-> 10
2 <-> 7
2 <-> 8
3 <-> 11

I want to be able to get(7) -> returning 2 and get(2) returning [7, 8]. Is there another library out there which has a data structure I can make use of?

If not, what do you suggest is the better option to handle this case? Is keeping two Multimaps in memory one with and the other with a bad practice?

P.S.: I have read this question: Bidirectional multi-valued map in Java but considering it is dated in 2011, I thought I'll open a more recent question

Answer 1

What do you mean by

Guava has a BiMultimap class internally but didn't outsource the code

The code of an implementation is here.

I didn't check if this is a working implementation, nor if it made it into a release or if I'm just looking at some kind of snapshot. Everything is out in the open, so you should be able to get it.

From a quick glance at the source code it looks like the implementation does maintain two MultMaps, and this should be fine for the general case.