It was a good phone interview coding question, but there was almost no communication throughout the whole process. I talked about the solution and thinking process, and the interviewer seemed uninterested.

This is the first time I've wanted to hang up in the middle of an interview, seriously.

Well, at last, out of courtesy, I should have asked some questions, so I did. She said there was not much to talk about.

Well, that's my experience. I would not recommend this company to anyone.

Implement BigInt subtraction.