There's a rich tradition in the Clarkson Open Source Institute of identifying these "O(fuckit)" algorithms, because by the time you've asked the question, it's too late to spend any computation getting the answer, so the only possibility for O(0) is an algorithm you never run because the only answer you can get is a shrug and "fuckit". Unfortunately the wiki documenting examples is offline...
To put it another way, "What's the class of algorithms where writing down the input string inherently already provided the answer (so clearly you already knew it, why did you bother to ask?)"
Slightly different than the class of stupid bullshit you shouldn't have been doing in the first place :)