I applied for the job online and was contacted by the recruiter. She set up a technical phone screen with a software engineer, which was conducted on HackerRank. You are given a question and are required to implement a function to complete a given task. The question was easy, I would say LeetCode easy level.

Several days later, the recruiter set up a 1-on-1 "life story" interview. This interview was 30 minutes and conducted via Google Hangouts. After the interview, I waited one week for an update and then sent an email asking for one. Three weeks passed with still no response. Two months passed, and the recruiter finally sent me a generic email stating they would not be proceeding with me.

Overall, it was a decent experience, but the communication on the recruiter's part was terrible. She would not reply to any of my emails. I asked for feedback after receiving the rejection email, and I still received nothing. This shows me that they don't truly respect the candidates' time.

Write a function to validate the checksum in a UPC code.