PhonePe Lead Software Engineer Interview Questions and Answers for Experienced

Basic puzzles of medium complexity level. No improvement required

DSA questions of easy level. Asked for memory optimisations.

Q1. High level system design of wallet payment system, took example of paytm. This was hld questions so just basic components
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Q1. Low level system design of parking lot system
Ans. 
Design a parking lot system at a low level
• Divide system into components like parking spots, ticketing system, payment system

• Implement data structures like queues for managing parking spots

• Use algorithms like least recently used for spot allocation

• Consider scalability and performance in design
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Q2. Review of one of my projects at past company
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Q1. What is collection framework?
Ans. 
Collection framework is a unified architecture for representing and manipulating collections of objects in Java.
• It provides interfaces (like List, Set, Map) and classes (like ArrayList, HashSet, HashMap) to store and manipulate groups of objects.

• It allows for easy manipulation, sorting, searching, and iteration of collections.

• Collections in the framework can store objects of any type, including user-defined classes.

• Exa...read more
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Q2. What is spring boot dependency injection?
Ans. 
Spring Boot dependency injection is a design pattern where objects are passed their dependencies rather than creating them internally.
• In Spring Boot, dependency injection is achieved through the use of @Autowired annotation.

• It helps in achieving loose coupling between classes and promotes easier testing and maintenance.

• Example: @Autowired private UserService userService; // Injecting UserService dependency
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Q3. What is the use of rate limiter?
Ans. 
Rate limiter is used to control the rate of incoming requests to a server or API.
• Prevents server overload by limiting the number of requests a client can make in a specific time period

• Helps protect against DDoS attacks by limiting the rate of incoming requests

• Ensures fair usage of resources by preventing one client from monopolizing server resources

• Can be implemented using algorithms like token bucket or leaky bucket

• Ex...read more
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Q4. What is the mean by thread, how many ways we can create thread?
Ans. 
A thread is a lightweight sub-process that allows concurrent execution within a process. Threads can be created in multiple ways.
• Threads can be created by extending the Thread class in Java.

• Threads can be created by implementing the Runnable interface in Java.

• Threads can be created using thread pools in Java.

• Threads can be created using asynchronous functions in JavaScript.
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Q5. What is use of thread.join()?
Ans. 
thread.join() is used to wait for a thread to finish its execution before moving on to the next steps.
• thread.join() blocks the current thread until the thread it is called on completes its execution.

• It is commonly used in multi-threaded applications to ensure that all threads have finished before proceeding.

• Without thread.join(), the main thread may continue executing while other threads are still running.

• Example: thre...read more
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Q6. What is the difference between sync and asynchronous call?
Ans. 
Sync call blocks the execution until the response is received, while asynchronous call allows the program to continue executing without waiting for the response.
• Sync call blocks the program execution until the response is received

• Asynchronous call allows the program to continue executing without waiting for the response

• Sync calls are easier to understand and debug, but can lead to performance issues if used excessively

• ...read more
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Q7. How to deploy your service in production server?
Ans. 
Deploying service in production server involves building the application, configuring the server, and monitoring performance.
• Build the application code into a deployable package (e.g. JAR file for Java applications)

• Configure the production server with necessary dependencies and environment variables

• Deploy the application package to the server using tools like Docker, Kubernetes, or manual deployment scripts

• Monitor the ...read more
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Q8. What is use of Jenkins and kubernates?
Ans. 
Jenkins is a continuous integration tool used for automating software development processes, while Kubernetes is a container orchestration platform for managing containerized applications.
• Jenkins is used for automating the building, testing, and deployment of software projects.

• Kubernetes helps in automating the deployment, scaling, and management of containerized applications.

• Jenkins can be integrated with Kubernetes t...read more
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Q9. What is the difference between fail safe and fail fast
Ans. 
Fail safe focuses on ensuring system stability and preventing catastrophic failures, while fail fast prioritizes quick detection and response to errors.
• Fail safe is about designing systems to minimize the impact of failures and ensure stability.

• Fail fast is about quickly detecting and responding to errors to prevent further issues.

• Fail safe often involves redundancy and error checking mechanisms to prevent catastrophic...read more
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Q1. One leetcode easy-medium problem
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Q2. Java, springboot and oops question
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Q1. Project related questions
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Q2. System design questions
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Q1. Design Search Engine
Ans. 
Design a search engine
• Consider using web crawling to index pages

• Implement a ranking algorithm like PageRank

• Include features like autocomplete and spell correction

• Support advanced search operators like boolean operators and filters
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Q1. Question related to JD linux shell script
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Q1. Related to salary discussion, Timming for the job
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Q1. Question related to old company project
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Q1. What is java multithreading
Ans. 
Java multithreading is a feature that allows concurrent execution of multiple threads within a single process.
• Multithreading in Java allows multiple threads to run concurrently within a single process.

• Each thread has its own stack and executes independently, but shares the same memory space.

• Java provides built-in support for multithreading through the java.lang.Thread class and java.lang.Runnable interface.

• Multithreadi...read more
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Q2. Explain exception hierarchy
Ans. 
Exception hierarchy is a way to organize and categorize different types of exceptions in a software system.
• Exceptions are organized in a tree-like structure with a base class at the top and more specific exception classes below.

• Base class usually is 'Exception' or 'Throwable', with more specific classes like 'IOException', 'NullPointerException', etc.

• Subclasses can provide more specific information about the cause of t...read more
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Q1. Given a code snippet, do code review and provide all the improvements. Mainly they look at how well you can catch the logical errors over minor improvements
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