Nice that you don't keep a reference to List<I> collection in the constructor, only the size of the collection. You don't need the collection itself, only the size (unless you do it the way barrysweeny did
https://www.codewars.com/kata/reviews/549682b0f025f497750000a8/groups/5e90303edf143800016b578f)

The naive approach is to make your md5Hash function return a 32 character string, and compare it to the hash that was sent to the function.
Strings are slow. Try to compare byte buffers or arrays.

Not bad

It's worse than that--the problem statement implies that m will be nonzero: "Your task is to return to the function seven(m) (m integer >= 0)"

I like this solution best, because it works when n and m are negative (although the problem statement claims the inputs will never be negative).

Not true. If n or m are 0, first if will be true, and return 0

One thing that is not made clear in the instructions: The final number might be negative

If you start with 109, then the next number in the sequence is 10 - 2*9 = -8

assertArrayEquals(new long[] {-8, 1}, DivSeven.seven(109));