A phone interview required solving a coding problem (coding, compiling, creating your own tests, and running them) within 40 minutes. The coding itself was not difficult, but the testing phase lacked clarity. The interviewer did not mention how to process the input.

The interview primarily aimed to assess if you could code quickly and cleanly (bug-free). They did not seem to consider industry experience or other resume details. As long as you could code, you would be considered suitable. It appeared a junior person conducted the interview, occasionally making incorrect comments about the code. This might have been part of the interview process to gauge how you handle vague or incorrect problem descriptions.

This is not a hard problem. You need to implement a Java class with a few APIs to solve a practical problem.