Also we can wrap this by function for optimization purposes ;) thanks for the replies

Thanks, my bad.

Yes, just like in my example.

https://jsperf.com/wubstep/12

Mutation of the input isn't that great but variable as a second argument looks nice

Global " i " is not good

It's a really cool trick to make recursion look "pretty" with this one time argument after the function.

Awesome task.

It will be harder to read.

Nice, so it's legit to use in every task? :D

Thanks for your answer, can you explain more detailed, why has is better, cuz i thought that has should iterate through Set as well as include through an Array. For me there is no difference in those operations.