Paypal Interview Experience for SSE

Round 1: Hacker rank round: I don’t remember the questions.

Round 2: Technical Round 

• Brief Intro
• Given an unsorted array arr of size N of positive integers. One number ‘A’ from set {1, 2, …N} is missing and one number ‘B’ occurs twice in the array. Find these two numbers.
• You are given N elements and your task is to Implement a Stack in which you can get minimum element in O(1) time.
   

Round 3:System Design 

• Brief intro, 
• Have you worked on Multi-Threading
• Producer-Consumer Model
• Method of threads
• How to wait and notify different from sleep
• How to make a class immutable, give an example transaction
• Transaction related question from Spring
• What is spring AOP, type of AOP
• Internal Working of HashMap
• What is Optional, why it is used
• Difference between Abstraction and interface, Give a real-life example
• Any design pattern used -> Factory pattern lld
• HLD -> design an e-commerce application like amazon Flipkart

Round 4:Techno Managerial Round

• The description is given by Director on Paypal, project scope, and tech stack
• Detailed discussion on experience, all projects 
• Behavioral questions 
• Best learning so far
• new tech stack learned
• Team structure
• How SDLC is followed 
• Coding question 
• How to make a class immutable, give an example
• Use of static, final 
• Design a class Age Calculator with all corner cases covered which take input dob and return age. 
• Make AgeCalculator immutable.
• Design your hashmap, in which we can use all hashmap functions, but double size should be returned.  -> use composition
• Design Rubix cube as a real-life entity.