Meta Software Engineer interview questions

Was contacted by interviewer on LinkedIn. Since I live in Seattle, I was called onsite for 45 min preliminary round. HR received me and gave office tour. Then, I was introduced to interviewer. Interviewer was young and energetic . Interviewer asked me a question around binary tree and I was able to answer the question and write code quickly. Next day I was contacted by recruiter saying that they want to scheduled another interview before calling me onsite. This time I asked for phone interview. Second interviewer asked another question related to trees. I was able solve the problem and write code in 40 min. Later HR contacted me and said Interviewers are not happy with me. I'm not sure what they were expecting. HR said they couldn't tell me the reason for rejection due to legal reasons. It seems like they just want young engineers who can just code.

The recruiter first asked me about the project. That took about 5 or 7 minutes. Then he asked to solve one coding problem. I successfully described the most efficient solution. However, it took me way too long, so I ran out of time before getting even halfway though the implementation.