Can companies use code that I wrote during a coding interview in their products?

Question

Suppose a company's programmers are struggling to code a portion of a complex program. HR orders the questions of an upcoming interview to be replaced with that of the unfinished complex program. It is never mentioned in the new question's statement that the applicants are dealing with a real problem rather than an artificial one made just for the purpose of the interview.

Due to the high difficulty, only a handful of candidates successfully solved parts of the problem. While none of their solutions would complete the program alone, when combined they would make a nice solution. CEO decides to do just that but does not hire any of those interviewed, instead have the developers copy-paste then modify the answers those interviewed presented in order to cut costs. Can companies do this without giving any compensation to the code's original writers?

Answer 1

CEO decides to do just that but does not hire any of those interviewed, instead have the developers copy-paste then modify the answers those interviewed presented in order to cut costs. Can companies do this without giving any compensation to the code's original writers?

Copying it verbatim and then making changes would be clear breach of copyright. The rights to that piece of code, unless otherwise contractually agreed upon, remain exclusively with the writer.

However, someone already mentioned, software development does not work that way. It would be absolutely fine to read all the candidates solutions, understand those solutions and then craft your own solution based on that.

That is why copying code from Stack Overflow verbatim is a problem (you would need to abide by the CC BY-SA license) while learning from it and then writing proprietary code with no attribution is fine and expected.

Copyright only protects the exact expression, not a vague idea.

For example were are allowed to make use of maths or the English language, despite the fact that we learned it in school from books that were copyrighted.

It would be a breach of copyright to copy those books, it is not when you simply use what you have learned from them.