Google Senior Software Engineer interview questions

I was contacted by Google recruiter and went directly with on-site interview because (I think) strong internal referral. I spent a week preparing the interview. On interview day, there were 5 rounds of technical interviews + lunch. 9 questions in total, I answered all of them correctly, although one of them I figured out it's DP but didn't have time to figure out details because I was only given 5 minutes to work on the problem ( the next interviewer was waiting). I did use hints for solving some of the problems. I felt really good about the interview. A week later, I got rejected and recruiter said she couldn't give me any feedback. I can only think of two possible reasons for rejection: 1. They only hire engineers who can come up with perfect solution in 5 minutes which is not what they claim in interview tip video that they want to see the brute force solution first and they want to see the analytical skills. 2. They rejected me for factors outside of interview I felt the 2nd reason is more likely for my case and they rejected me due to my experience, age, and/or lack of ivy league education. In the past I got offer by top company with worse interview performance. This is ridicules, they seem to have a mysterious formula to determine whether you are a good fit. They can pretty much figure it out from my resume, why waste my time and energy on the interview! It cost me $500 to take PTO.