We know that the signature should always be 3 numbers (r, g, b). So, I’d find it a bit dangerous and unnecessarily "clever" to spread the args like that. Plus, it’s now unclear from the consumer’s side what the arguments are supposed to be.

weird.

this is nice, didn't think of

Explanation much appreciated!

If you'd check if num is even than you could iterate with i+=2 instead of i++ and get x2 times faster solution

This is great. I didn't know you could pass a radix to the #toString implementation on a Number object. Really appreciate this solution.

I like the chunk idea :) It'll change 'numbers' for the caller, but it's super clean to read.

They are less than 2 (and not prime). A prime is a natural number greater than 1 that has no positive divisors other than 1 and itself.

What about all negative numbers?

I really like such kind of kata, good description, includes tests... but mostly because it looks easy when reading the description but than it develops into a real brain teaser when you're on it. And thanks for reminding me how much I hate date and time manipulation in JS ;-)

Your second example in the description is contradicting with your code example, if I understood it right the code example should be:

array_diff([1,2,2], [2]) // [1]