Meta Software Engineer - Internship interview questions

Everything was great until I had the phone interview. It was by far the worst phone interview experience I've ever had. 1) The interviewer did not speak English well and refused to move to a more quiet location. 2) The problems were easy, and after getting solutions the interviewer asked me to make impossible optimizations. It is IMPOSSIBLE to do this problem O(1) space; in fact, the interviewer's on solution runs in O(n) space. But apparently I had to do this, even though I had a working O(n) space and time solution 5 minutes in. If my interviewer does have a working O(1) solution for this, someone should award him the Turing Prize.