Booking.com Software Developer interview questions

My friend applied for me as a software developer. I got 4 problems to solve in 75 min on hackerrank it was easy. After that, the recruiter called me that I passed the first phase and asked me why I applied to booking and what I'm expecting and told me that there will be phone interview contain two problems and I will solve it in codepad the idea should be correct and will discuss about the complexity. I passed this interview it was interesting the recruiter called me again and told me about the onsite interview. I get prepared for this step and study system design and solve problems, read in the data structure, She sent to me some useful links to look at. I went to Amsterdam it was a great city to live in it. The interview was 3 phases( algorithms and data structure, system design, culture fit) The algorithm was an easy problem I found the optimal solution for it but will I'm talking they ask me some questions that I didn't know exactly the answer. The system design was good and it was my first time to know about system design. and I failed in the culture fit interview and that was a surprise for me. But it was a great experience and I will apply again when it's available.