The default sort is ascending. The minus makes the greater numbers smaller, e.g. 10 is greater than 5,
but -10 is less than -5. Minus naturally reverses the order of sort. Got it?

Don't feel bad about your if statement, this solution with an unnecessary dict creation is slower than your if block.

Triangular numbers and algebra

Because your function isn't returning a number as it should.

Python ignores it.

In the following code:

def f(x) -> int:
    return int(x)

the -> int just tells that f() returns an integer.

More information here PEP 3107

@Steffan: when you mark your post as spoiler, the person to who you answer doesn't get any notification. That's why you see sometimes this kind of message.

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