Tesla interview questions

This was my first phone interview. We did a Google-docs type thing with speaker phone. Found by recruiter, submitted updated resume/cover letter. About 2 weeks later (to my surprise) a phone interview was scheduled. Had a nice chat with the head of Interactive Software, then was given a Google-docs question: wrote code to enumerate all possible alpha-phone codes given a number. After about 15-20 minutes I wasn't able to figure it out. Very irritatedly he said something like "well, everybody has to do it. good luck to you, bye". I don't know if it's customary for the interviewer to be that terse/to say goodbye after a single question, but I found it to be rather rude and shortsighted. Would be curious to hear other people's opinion about that.