Did the Booking.com coding rounds last month, both the automated online assessment and the live technical screen. Sharing because I couldn't find much detail on the OA specifically.
Online assessment (OA): Invited via HackerRank link after the recruiter screen. Two questions, 90 minutes total. Both were algorithm problems, not system design or SQL. I got one on array manipulation (essentially a sliding window variant) and one on trees (find the paths meeting a certain condition). Both felt like medium difficulty on leetcode. I've seen people say they got a hard but I did not. Maybe it varies by role or cohort.
No proctoring video in my case, just code in the browser. You can use your preferred language. I used Python.
Live coding rounds (two in the full loop): These felt different from the OA. They were more conversational. Both interviewers started by reading out the problem and explicitly said "talk me through your thinking before you write anything." I think they care more about how you approach it than getting to the optimal solution in record time.
First round: string manipulation problem. Pretty standard, not tricky. I solved it cleanly in about 20 minutes, rest of the time was talking through edge cases and a follow-up variant.
Second round: graph problem, basically shortest path with some constraints. I took a BFS approach and explained why. They pushed back gently and asked if there was another approach. I walked through Dijkstra briefly and we discussed the tradeoffs. I didn't code the second approach, just reasoned through it.
What I'd tell someone prepping: do 60-80 mediums across arrays, strings, trees, and graphs. You're not going to see a hard in the coding rounds from what I can tell. The live rounds really reward clear verbal reasoning. If you go quiet and just type, they will ask you to explain yourself.
The behavioral question I got in the coding round (yes, there was one wedged in): "Tell me about a time you caught a bug in production. What did you do?" Classic Booking structured behavioral.
Happy to give more detail on either round.