It is clever, but not the best solution as no one understands with a brief look what's going on.

Fixed, thanks for pointing that out

you are lost final XD;

nitpick: a minor typo in the descirption to represent empt[I]ness

Holy smoke.... this is genius code x.X

Nice solution

cool

I have not seen such a method in any book, even searches on the Internet have not yielded results.

where do you find all this? XD

Woah! can you explain so i can learn

What will happen in if n is 0?

It is a nearly perfect solution.
You can be a bit concise by using the reduce method instead, because it uses the first value which is identical here.

fun fact(n: Int): Int {
    return (1..n).reduce { acc, i -> acc * i }
}

here indexOf does not reduce the speed too much?

You fork it (The button on top right) and then you can run it.

For what reason was static removed? How does that help?