PayPal Interview Experience for Backend Java Developer (2.5+ Years Experienced)

Hi Folks, I was interviewed recently at PayPal for the role of Backend Java developer (Software Developer). To give an overview, I have an experience of 2.5+ years of. 

Round 1: OA(HackerRank) 3 medium-hard level questions based on dynamic programming and Strings manipulation. In all the questions, all test cases were passed. On the same day by evening, I was informed that I have cleared OA and they would be scheduling 3 or more interview rounds after a week. Each round would be an elimination round.

Round 2: DSA + Algorithms

1. Given a board of m*n having characters ‘+’ and ‘0’, source, and destination. Calculate if we can reach from source to destination given that we cannot move to the ‘+’ cell (A traditional BFS/DFS problem). It was later modified to – we can exit from any boundary where boundary cell is 0, calculate min moves. 
   https://www.geeksforgeeks.org/check-possible-path-2d-matrix/
2. Find intersection in multiple LinkedList when nodes can have duplicate values. We then discussed the concept of sequencing.
   https://www.geeksforgeeks.org/write-a-function-to-get-the-intersection-point-of-two-linked-lists/
   

Round 3: Core Java coding + LLD

1. Set s = new TreeSet<Object>()
      s.add(10)
      s.add(“ABC”)
      s.add(new User())
   
      Will this work? No, it will throw ClassCastException.
2. Find the last 3rd node in LinkedList. I was later asked to write a generic code where we can find the last k element in any LinkedList.
   https://www.geeksforgeeks.org/nth-node-from-the-end-of-a-linked-list/
3. LLD : Login + SignUp + Profile page(REST API)
   The design should support Authentication and authorization of users (I chose spring security). I had to define classes, methods, DB tables, and choice of DB (I chose MongoDB because it’s cheap).
   Later I was asked questions about how will I handle multi-threading and scaling.
   

Round 4: Hiring Manager discussion

1. Detailed discussion on Projects.
2. Most challenging one
3. Detailed discussion on features of Java 8
4. Stateless REST
5. Testing frameworks
6. We use SonarQube for code quality checks, so questions related to that.

Verdict: Selected