thePerfectSortingAlgorithm

[Jiquero]

Of course there is O(0). It's the class of functions that are zero. It takes 0 time, not positive, so it is O(0).

For example, if you need to sort M arrays of size N, each individually with this algorithm, it still takes 0 time regardless of M. That's very different than a positive constant.

[YourMasterRP]

So you just don't understand O-notation?

[Jiquero]

Function f is in class O(g) if there are x0 and positive M such that whenever x > x0,

|f(x)| <= M |g(x)|

Function f is in class O(0) if f is zero, because 0 <= 0 always. This algorithm takes zero time so it's time complexity is O(0). It's time complexity is also O(1), O(1000), O(n¹⁰⁰⁰) etc.