IANAL, but nearly any recorded/written down is copyrightable. However ideas are not. If you implement from pseuso-code, it is another expression of the same idea. Different forms of expression have different rules on how different the new work must be to be unique. If you copied a function and just changed the variable names, it could be argued that it was an infringement.

If you copy a compilable function and give attribution, probably no one will care. If you copy a whole enterprise system, they might. If the original author cares, there should be a rights notification in the code. In particular Wikipedia articles have the GNU Free Documentation license, so you are pretty safe there.

The Wikipedia license is a copyleft license, which may present problems for software that is not open source.

I would also rather not credit a Wikipedia article in my closed source software unless it's really necessary.

Somehow I don't think Wikipedia would sue you for implementing their pseudocode.

I would rather credit Wikipedia as the source of a common "well-known" algorithm than leave the door open to claims from some third party.

Copyrights protect original works of authorship fixed in any tangible medium of expression. Copyright protection also extends to derivative works. If a new work is transformative when compared to a parent work, the child work is not considered derivative. In that case copyright doesn't extend to the child work. In the opposite case the opposite would be true.

So the issue is whether an algorithm implementation is transformative when compared to the pseudocode.

The answer to your main question is fact specific. Each case is different and a court of law will look at the specific facts and make a ruling.

Talk to a lawyer for counsel that relates to your specific facts.

Pseudocode is an informal representation of an algorithm using informal language. Not only is that copyrightable since it is an original work, but I would also argue that it could be patentable because the underlying algorithm is patentable.

Scribbles are copyrightable.