What is the fastest way to check that 2 collections (lists with possible duplicates) have same content? 1. two containsAll calls 2. intersect and check size to each set 3. union and check size to each set 4. union size same as intersect size 5. anything else?

Only 10 elements? Then this seems like premature optimization.

Time for JMH 😂

yes, same amount of copies for duplicates

Do they need to have the same amount of duplicates ?

You are absolutely correct. Sorting and comparing one by one from both lists would be faster. Thank you!

Fyi two containsAll even don't work - false positive for [a,b,b] and [a,a,b]

In fact, none of the options work except for the sort/compare option, due to duplicate handling.

Another option to maybe is try is convert both to a bag, a

Map<T, Int>

and compare those for equality, which should be

O(n)

in total I think. Probably not worth it for 10 elements.

I don’t undertand the use case, are you trying to remove duplicates for each list or both lists combined ?

It is part of .equals(). I'm not trying to modify collections.