for 50, your code will return XXXXX (5 Xs, each representing a value of 10) whilst the correct output should be L . The same also applies for other interval checking points greater than 10.

I am reading about regular expressions now, it starting to make sense. Thanks!

This is the syntax of regular expressions, you have to search about this topic if you don't know it.

This will add a space before every capital letter regardless of whether it is part of a camelcased word...

I benchmarked it and found it to be at least twice as slow as the ternary implemenatation. It looks nice though.

Agreed. Codewars uses Ruby 2.1.6, and this issue is not fixed until 2.2

The random tests fail because although -3 should return false, Ruby 2.1.6
sees it as -3.abs.prime?, where "self" is just 3.

I filed a suggestion on this kata... IDK how much the author can do about this.

It's a question of what's more idiomatic. See Avdi Grimm's master work: Confident Ruby

Which version of Ruby do you have locally? My Ruby 2.0.0 return false for negative numbers.

This didn't work for me because many of the tests are random and Ruby's stdlib Prime will return true for negative numbers when the absolute value is prime, but the test is not expecting it.

The description specifies: "Input will always be a non-negative integer."

Don't think this solution is correct: when n and m are both negative, this solution will give you the positive result, when 0 should be returned.

This is my favorite answer, grats for making me laugh :D