I recently applied for software developer roles in London and got offers from Amazon, Google and Facebook. I wanted to give back to the community and share my experience.
I have 2 YOE working in a startup in Bangalore.

Amazon Onsite:
Each interview had few behavioral questions and 1 coding question.

Time when you dived deep; Design elevator system
Time when you made a mistake, decision you made which conflicted; Hangman guess to minimise number of guesses
Hurdles in the project, ownership (something did out of scope); packages dependency (topological sort)
Most challenging proj; Find function of linux

Google Onsite:

1. https://leetcode.com/discuss/interview-question/317383/Google-onsite-Divide-points-into-two-equal-halves
2. Small variation of distance-nearest-cell-1-binary-matrix from geeksforgeeks
3. Given array of statue heights, and an array of cave heights, find max number of statues that can fit in the cave. You can only insert into the cave from the opening (which is at index 0), and slide as necessary.
4. Have a story which 1 person knows, there are meetings between 2 people at some timestamps where they share this story if they have been told before. Find who all know the story at the end. Follow up: what if the timestamps can be same for few meetings
5. Googleyness: time when you adapted a piece of code from other team’s code, most challenging proj, a proj where the requirements were not clear, plan an offsite for your team, how to solve conflicts with peers
   There were follow ups in each interviewers which wanted to optimise my code further and think of different approaches.

Facebook:

Screening round:
I was asked 2 questions:
A slightly modified version of https://leetcode.com/problems/random-pick-with-weight/
https://leetcode.com/problems/k-closest-points-to-origin/
Was able to solve both, but took some time in explaining and dry running the 1st solution due to which couldn't explain 2nd question properly.
Onsite:
I was asked 2 graph questions in each of the technical rounds. In system design, I was asked to design Instagram.
I don't remember the exact questions, but they were Leetcode medium (unlike Google). For facebook, I feel the focus is more on coding quickly without making mistakes.

I finally decided to go with Facebook.

Preparation: I did around 100 leetcode questions (70% medium, 30% hard), studied DDIA and Sys des interview.