If somebody answers by just putting a link, is the answer acceptable?
Should the answer be flagged as "not an answer"?
This has been covered numerous times previously; the most thorough being the MSO post, Are answers that just contain links elsewhere really "good answers"?
Short version: it's a really bad idea.
A link isn't an answer; it's just a pointer to a possible answer. With no context, someone seeing just a link doesn't know if it might be on-topic, off-topic, a joke, or spam. Even a little bit of context helps make it clear why the link is worth following.
Additionally, answers here should be for the long term. If someone has the same problem two years from now, the link that's currently to a great blog post may well later be a 404 (or worse). If the link was the entire answer, then Apple.SE no longer has an answer for the question.