I used map to create a look up table. The interviewer was not amused. I told the interviewer about approach and time complexity would be O(n). The interviewer did not even allow me to write the code, just said "Thank You for your time". Did not even allow me to reply back and disconnected the call. Although another 10 mins were remaining in the stipulated time. One of worst interviews ever. Walmart being such a good brand, never expected this.