Round 1 (45 Mins)
Brief description of the current project: Architecture, Technologies, Workflow etc.
 A 2D array problem(cant remember exactly) but I have to sum up the values on given constraints: He asked to start with basic approach so I gave O(n^4) time complexity solution then he asked for improvisation, after some workout I came up O(n^2) time and O(n^2) space complexity solution. He asked for more optimisation (avoid extra space) but in given time I could not find solution without extra space.
 Find the difference between sum of values in odd level and sum of values in even level in given binary tree: I explained the approach then he asked me to write code with both recursive and nonrecursive approach.
Solution: GeeksforGeeks Link
Round 2 (50 Mins)

Tapping Rain Water problem: I didnt know the classic solution but I came up with my own approach which worked fine.
Solution: GeeksforGeeks Link
 A 2d array with all 1s and 0s where 1s are land and 0s are water, Matrix itself is surrounded with water i.e 0. I gave him O(n^2) time and O(n^2) space complexity solution and he accepted.
He asked questions like most challenging task you did in your past experience, I explained him about middlewares I implemented earlier for tracking the exceptions in code.
Round 3 (written)
I was called in Amazon office after few days (very nice office)
 Tree traversal with several ways.
 Few linear array problem
I believe this round was just for warmup.
Round 4 (45 Mins)
Brief description of current project: this time he was more focused on technologies and tools. He asked every technology I mentioned in deep.

Top view of given binary tree.
Solution: GeeksforGeeks Link 
An html format string was given where I have to find output of given queries.
Ex.Pratik
Queries would be like: GET name, so output would be Pratik. (something like that)
Round 5 (Manager)
 After some formal discussion he came up with his question “Design pattern for chess game” for which I wrote few classes and explained approaches for the game like peer to peer and clientserver but he was not satisfied. This round didn’t go well.
I could not make it but it was very good experience, All interviewers were so friendly and helpful.