I could not believe my eyes indeed, I dunnot about 20x but I got 8x faster 265k & 288k op vs 2.3M

Lol why? xD

Where do you want to place ++i ?

:)

:)

Becuase there is no 'length' propertie for Sets

Welcome & ty

You can actually use a binary search approach, since items are sorted here.

In C++ you would get it easily with lower_bound.

have you actually tried to run the code?
it outputs: [2, 3, 4, 5, 6, 7, 8] not [2,4,6,8]

9 - 2 = 7 (not 4)

Pippi is the name of my (late :( ) cat; being not a method, it just throws an error, as expected by the specs.

Unreliable rounding and needless conversion to string.

Thanks. To be honest I don't know how you call this (backreference?), but $1 refers to the first group in the regex => (^.+) and $2 to the second group => (.+$)
Whatever it matches will be printed straight into the return string. This one's with back-ticks, but that's not really necessary.