Round 1: Written test with 2 questions

1. Given an array of size n containing both positive and negative numbers. Find the count of subarrays whose sum is 0.
2. Add next pointer to every node present at the same level.

Round 2: Data structures and Algorithm

First discussion on my approach and code for the written test problems
1. Minimum number of platforms required for railway-bus station
2. Given a chess board of size m*n. A knight is present at some initial position. Find the minimum number of moves so that it can move to some given final location.
   Hint: Think BFS

Round 3: Algorithm, Design and OOPS concepts

1. Design a tank game. 

   HLD and LLD with classes and functionalities. Design patters, abstract classes and interfaces

2. A continuous stream of numbers is coming. Find the median at any given time. Algorithm and code

   Hint: Lets say m is a median at any given time. Use a min heap of numbers more than m and a max heap of numbers less than m. Now retrieval is O(1) and insertion is O(log n)

3. Design whatsapp. Just high level design
4. How deployment works on multiple server machines. Concepts of AB testing and few other questions

Round 4: Algorithm, Design, multi threading, concurrency, database concepts

1. Question 1: Given a string of characters. You need to transform it to a given new string of same length in minimum cost where:

   a) ‘b’ can be transform to ‘a’ or to ‘c’ with cost 1. Similarly for other characters.

   b) any numbers of b’s can be transformed to c’s with cost 1 and also to a’s with cost 1.

2. Given multiple bars of given heights and unit width. Find the rectangle with max area.
3. Design a vending machine
4. How will you choose which column to choose for indexing.
5. Sharding in databases. How facebook would shard it users database
6. Questions on mulithreading, immutable class, concurrency

Round 5: Design, Previous experience and practical questions

1. Explain any 1 project I enjoyed working on

   Interviewer was not interested in my project and moved to a design question

2. Design a traffic signal starting with all use cases, HLD, LLD
3. Design an elevator system

   My favorite design patterns and what patterns I would use in above questions

What I would look in design reviews and in code reviews and few other behavioral questions

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