I agree that such questions are low-quality. I think the current options take care of these cases pretty well:
They usually show no effort in asking the question
Downvoting is appropriate for such questions. In fact, the first part of the downvote arrow's tooltip is "this question does not show any research effort." Note that it's possible for a question to be entirely on-topic and well-phrased (therefore not being a good candidate for closure) but still be of poor quality.
They [...] are hard to answer because it is not totally clear which variant of the algorithm / which facts about the algorithm the OP knows.
These are a perfect application for the "unclear what you're asking" close reason, which asks the author to clarify. Note that it's possible for a question to be on-topic but still unclear or overly broad.