Thanks for the suggestions!

If you think of any random test cases/edge cases, I'd definitely like to add some.

With the solution I have, it'd just be duplicating everything (with negatives & 'in' instead of 'ago') - unless someone comes up with a solution that incorporates it I won't worry about it for now! Thanks though :)

Good catch. Did you add this test case?

tricky, but good kata!