Absolutely. Best solution of all.

I like the logic behind your solution. Very similar to mine

what about now

yes. apparently the tests don't catch O(n^2) solutions despite the description.

No, it doesn't.

Here's a profile of running this problem 10 million times with an if/if/if solution versus an if/elif/else solution:

if_if_if completed 10000000 iterations
Sum time: 5684.13ms
Mean time: 568.41ns
Standard deviation: 1684.53ns

if_elif_else completed 10000000 iterations
Sum time: 5685.18ms
Mean time: 568.52ns
Standard deviation: 1642.49ns

Even if it did, if you care about nanoseconds you shouldn't be choosing different flow control syntax in Python, you should be choosing a different language.

if elif else statement works faster than if if if

Because you have to do a lot by hand, it's really usefull !

Many methods in Python take an iterable as their argument (this is usually noted in the signature description in the documentation). A generator expression is, much like a list, iterable. Therefore it is not necessary to actually construct a list (neither explicitly or via list comprehension), in fact it simply uses up more memory.

Yes, it does work without square brackets. I just checked, because I got identical solution except of square brackets I got list(). After removing list() it still works.

why?

actually, there are useless sets in there too. See the fork to avoid them.