Mercari Senior Software Engineer Interview Questions and Answers

Q1. What is event loop, how it works.
Ans. 
Event loop is a mechanism in programming that allows for asynchronous execution of code by continuously checking for and handling events.
• Event loop is commonly used in JavaScript to handle asynchronous operations like setTimeout, setInterval, and AJAX requests.

• It works by continuously checking the event queue for any pending events, executing them one by one, and then moving on to the next event.

• Event loop helps in pre...read more
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Q2. Micro task queue and macro task queue.
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Q3. Is node.js single threaded or multi-threaded, also discuss threadpool and it's usages.
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Q4. Tell the order of output, among process, promise, setTimeout, fs, setInterval.
Ans. 
The order of output is fs, process, setTimeout, setInterval, promise.
• fs module is synchronous and will output first

• process is next in line

• setTimeout will be executed after process

• setInterval will be executed after setTimeout

• promise will be executed last
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Q1. JavaScript usages compiler or interpreter.
Ans. 
JavaScript is an interpreted language.
• JavaScript is an interpreted language, meaning it is executed line by line at runtime.

• There is no separate compilation step in JavaScript like in languages that use compilers.

• Examples of interpreted languages include Python, Ruby, and PHP.
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Q2. Tell the output among various for loops using var, let and bind.
Ans. 
Output comparison of for loops using var, let, and bind in JavaScript.
• Using var: variable is function-scoped, may lead to unexpected behavior in loops.

• Using let: variable is block-scoped, recommended for loop iterations.

• Using bind: creates a new function with a specified 'this' value and initial arguments.
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Q3. A medium level dsa question on array, solved it using pre-sum.
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Q4. Situation based question, on how to pick a suitable database.
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Q1. What do you do on daily basis, and how to decide a tech-stack on high level.
Ans. 
I work on coding, debugging, testing, and collaborating with team members. Tech stack decisions are based on project requirements, scalability, performance, and team expertise.
• Daily tasks include coding, debugging, testing, and collaborating with team members

• Tech stack decisions are based on project requirements, scalability, performance, and team expertise

• Consider factors like language compatibility, libraries/framewo...read more
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Q2. Design an online scalable, real-time document sharing application like google docs.
Ans. 
Design a scalable, real-time document sharing app like Google Docs.
• Use websockets for real-time collaboration

• Implement version control to track changes

• Utilize a distributed database for scalability

• Include user authentication and access control

• Support offline editing with automatic sync
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Q3. How to handle images also in the future.
Ans. 
Utilize cloud storage for scalability, implement image compression techniques, and regularly update image processing libraries.
• Utilize cloud storage for scalability

• Implement image compression techniques

• Regularly update image processing libraries
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Q4. Any other way to solve the problem, of high I/O on same document to overcome throughput and conflicts.
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I was asked question on sliding window on finding the largest subarray with all distinct numbers. The interviewer was very helpful.

Q1. Create a controller , service and repository methods and classes to save userDeatils in table using Spring Data JPA .
Ans. 
Create a controller, service, and repository to save user details using Spring Data JPA.
• Create a UserController class with appropriate mappings for saving user details.

• Create a UserService class with a method to save user details.

• Create a UserRepository interface that extends JpaRepository to handle database operations.

• Implement the saveUserDetails method in the UserService class to call the save method of the UserRepo...read more
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DSA, 1 hour with 2 LC medium questions

Q1. Low level design
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Q2. Design lld for Dream 11
Ans. 
Designing the low-level design for Dream 11 platform.
• Use microservices architecture for scalability and flexibility.

• Implement a robust database schema to handle large amounts of user data.

• Utilize caching mechanisms to improve performance, especially during peak usage times.

• Include authentication and authorization mechanisms to ensure data security.

• Design APIs for seamless integration with third-party services.

• Implement...read more
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Q1. High level design
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Q2. Design HLD for rider management system
Ans. 
Design HLD for rider management system
• Use microservices architecture for scalability and flexibility

• Implement user authentication and authorization for security

• Include features like ride tracking, payment processing, and feedback system

• Utilize databases for storing rider information and ride history
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Two medium DSA questions based on strings.

Q1. Design Google Meet
Ans. 
Design a video conferencing platform similar to Google Meet.
• Implement real-time video and audio streaming

• Include features like screen sharing, chat, and participant management

• Ensure scalability to support large number of users

• Focus on security and privacy measures

• Optimize for low latency and high quality video/audio
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1 hr, Java questions, SQL question, 1 DSA question

Q1. LLD about Hotel Booking system
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Q1. Discussed about the project
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Q1. Replace all zeros to 1 which are surrounded by 1's
Ans. 
Replace zeros surrounded by ones with ones in an array of strings
• Iterate through each string in the array

• Check for zeros surrounded by ones and replace them with ones

• Return the modified array of strings
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Q2. Minimum jumps to reach end of an array
Ans. 
The minimum number of jumps needed to reach the end of an array.
• Use dynamic programming to keep track of the minimum jumps needed at each index.

• At each index, calculate the maximum reachable index and update the minimum jumps accordingly.

• Example: For array [2, 3, 1, 1, 2, 4, 2, 0, 1, 1], the minimum jumps needed is 4.
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Q1. LLD Round:- Design classes for bidding system when new bid notifications shown to all users who already bided for it.
Ans. 
Design classes for a bidding system with new bid notifications for users who have already bid.
• Create a Bid class with attributes like bidder, amount, timestamp, etc.

• Create a Notification class with attributes like message, recipient, timestamp, etc.

• Create a BiddingSystem class to manage bids and notifications.

• Implement a method in BiddingSystem to notify users who have already bid when a new bid is placed.

• Consider usin...read more
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Q2. HLD:- Desing Post order service, or last mile like finding rider, notifications etc
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