oh my god how i missed this.
Really cool.
😌😉

Cool trick!

Very clever solution, however efficiency wise not really the best.

You end up going through the full list twice as well as doing two index calls.

The idea of converting the list to one of True, False is clever. Mine worked, but it was ugly compared to this!

I think the solution with computing all numbers isn't fit for the production based on the performance issue.

I don't like to wait too long (even a nanosecond).
But I like to learn new 1-line codes.

@daimonji, I had the same thought but did not know how to implement it. In your code, 'if poss[c]' is always False as both values in poss are equal to 0. Can you explain?

@Haksell, correct.

Yes, good idea. In my defence, I was not trying to come up with the absolute minimal solution when I wrote this.

I also didn't understand why they aimed for booleans

It does't change the fact, that variable name says nothing about stored content.