PayPal Software Engineer III Interview Questions and Answers

Q1. What are the best and worst solutions for the coding problem "Longest Substring Without Repeating Characters," including a detailed explanation of each solution along with their time and space complexity?
Ans. 
The Longest Substring Without Repeating Characters problem involves finding the length of the longest substring without any repeating characters.
• Best solution: Sliding Window approach with HashSet to track unique characters. Time complexity O(n), space complexity O(min(n, m)) where n is the length of the string and m is the size of the character set.

• Worst solution: Brute force approach checking all substrings for uniqu...read more
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Q1. Questions regarding Redis and cache eviction policies, and how would you implement a low-level design for the Least Recently Used (LRU) cache algorithm?
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Q1. What are software development design patterns? Can you explain singleton design pattern and code an example to show that?
Ans. 
Software development design patterns are reusable solutions to common problems encountered in software design.
• Design patterns help in creating maintainable, scalable, and efficient software.

• Singleton design pattern ensures a class has only one instance and provides a global point of access to it.

• Example: Implementing a singleton class in Java -

• public class Singleton { private static Singleton instance; private Singleto...read more
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Q2. Can you develop and simple API app to show its running and anyone request sending to it?
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Q3. What kind of databases you’ve worked on? And explain what is DML!
Ans. 
I have worked on relational databases like MySQL and PostgreSQL. DML stands for Data Manipulation Language.
• Worked on MySQL and PostgreSQL databases

• Familiar with writing SQL queries for data manipulation

• DML stands for Data Manipulation Language
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Q4. When we work with micro services , what is your experience which becomes challenge?
Ans. 
One challenge when working with microservices is managing communication between services.
• Ensuring proper service discovery and registration

• Handling network latency and failures

• Implementing effective monitoring and logging

• Maintaining consistency and data integrity across services
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Q1. What are the types of deployments?
Ans. 
Types of deployments include blue-green, canary, rolling, and immutable.
• Blue-green deployment involves running two identical production environments and switching between them.

• Canary deployment gradually rolls out changes to a small subset of users before deploying to the entire infrastructure.

• Rolling deployment updates a few instances at a time, ensuring continuous availability.

• Immutable deployment creates new instanc
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Q2. What is Blue Green Deployment ?
Ans. 
Blue Green Deployment is a software release strategy that reduces downtime and risk by running two identical production environments.
• In Blue Green Deployment, one environment (blue) is live and serving production traffic while the other (green) is idle and ready to be switched to at any time.

• This strategy allows for zero downtime deployments, as the switch between blue and green environments can be done seamlessly.

• Blue...read more
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Q3. I was asked travelling salesman problem to solve.!
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Q1. Tell me what you liked in last 2 rounds!
Ans. 
I enjoyed the challenging technical questions and the opportunity to showcase my problem-solving skills.
• Challenging technical questions

• Opportunity to showcase problem-solving skills
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Q2. Explain me the best project as per you which you worked upon and features of it.
Ans. 
Developed a web-based project management tool for tracking tasks and deadlines.
• Implemented user authentication and authorization using JWT tokens

• Integrated real-time chat feature using WebSockets

• Utilized React for front-end and Node.js for back-end development
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Q3. Some RegEx related questions were asked.
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Q4. How vector databases work?
Ans. 
Vector databases store data in a vector format, allowing for efficient querying and analysis of high-dimensional data.
• Vector databases use vectors to represent data points in a multi-dimensional space.

• They are commonly used in machine learning and data science applications for tasks like similarity search and clustering.

• Examples of vector databases include Faiss, Annoy, and Milvus.
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Q5. If I give you a coding problem to solve in the language you don’t know, can you solve it, when you’re allowed to refer Google search?
Ans. 
Yes, I can solve a coding problem in a language I don't know with Google search.
• Utilize Google search to understand syntax and concepts in the unfamiliar language

• Break down the problem into smaller parts and search for solutions to each part

• Refer to online resources, forums, and documentation for guidance

• Practice writing and testing code snippets in the new language before attempting the full solution
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Q6. How you can parse location and shop name from a card transaction string?
Ans. 
Use regex to extract location and shop name from transaction string.
• Use regular expressions to match patterns for location and shop name.

• Look for keywords like 'at', 'from', 'in' to identify location.

• Consider variations in transaction strings and account for them in regex patterns.

• Example: 'Spent $50 at Starbucks Coffee' -> Location: Starbucks Coffee, Shop Name: Starbucks Coffee
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A test that covers all fundamental topics, including networking, object-oriented programming (OOP), and data structures and algorithms (DSA).

Q1. Write code for quick sort
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Q2. Puzzle
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Q1. Explain the react lifecycle functions and how they work
Ans. 
React lifecycle functions are methods that are automatically called at specific points in a component's life cycle.
• Mounting: constructor, render, componentDidMount

• Updating: render, componentDidUpdate

• Unmounting: componentWillUnmount
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Q2. Css box model, difference between padding and margin
Ans. 
Padding is the space inside the border of an element, while margin is the space outside the border.
• Padding is used to create space between the content and the border of an element.

• Margin is used to create space between the border of an element and other elements.

• Padding affects the size of the content area, while margin affects the positioning of the element.

• Example: padding: 10px will create 10 pixels of space inside ...read more
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Q1. What are your salary expectations in CTC and variables?
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Q2. Will you relocate to the location required?
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Java coding questions, basic Java questions.

Q1. Java basics questions.
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Q2. Live coding.
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Q1. Discussion on previous experience and projects.
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Q2. System design question
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Q1. Questions on SQL, Java advanced, personal projects, Java frameworks, UI based questions, Agile methodologies.
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Q2. Interview discussion with the whole team.
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Q1. Benefits discussion.
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Q2. Salary discussion.
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Basic Oops MCQ and aptitude and one da

Q1. Basic dsa and project
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Q1. DSA and project related
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