Recro Mobile Application Developer Interview Questions and Answers

Round duration - 60 Minutes
Round difficulty - Easy

Q1. 
0/1 Knapsack Problem Statement
A thief is planning to rob a store and can carry a maximum weight of 'W' in his knapsack. The store contains 'N' items where the ith item has a weight of 'wi' and a value of...read more
Ans. 
Yes, the 0/1 Knapsack problem can be solved using dynamic programming with a space complexity of not more than O(W).
• Use a 1D array to store the maximum value that can be stolen for each weight capacity from 0 to W.

• Iterate through each item and update the array based on whether including the item would increase the total value.

• The final value in the array at index W will be the maximum value that can be stolen.
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Q2. 
Find the Second Largest Element
Given an array or list of integers 'ARR', identify the second largest element in 'ARR'.
If a second largest element does not exist, return -1.
Example:
Input:
ARR = [2,...read more
Ans. 
Find the second largest element in an array of integers.
• Iterate through the array to find the largest and second largest elements.

• Handle cases where all elements are identical.

• Return -1 if a second largest element does not exist.
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Round duration - 60 Minutes
Round difficulty - Easy

System Design Round

Q1. Design a system for Twitter, discussing its architecture, key components, and scalability considerations.
Ans. 
Design a scalable system for Twitter with key components and architecture.
• Use microservices architecture for scalability and fault isolation.

• Key components include user service, tweet service, timeline service, and notification service.

• Use a distributed database like Cassandra for storing tweets and user data.

• Implement a message queue like Kafka for handling real-time updates and notifications.

• Use a caching layer like ...read more
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Round duration - 30 Minutes
Round difficulty - Easy

It is just a formality

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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Sorting of an array and aptitude

Q1. BFS graph traversal
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Q1. Binary tree question
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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.
Ans. 
Choosing a database involves evaluating data structure, scalability, consistency, and specific use cases.
• Understand data structure: Use SQL for structured data (e.g., PostgreSQL) and NoSQL for unstructured data (e.g., MongoDB).

• Consider scalability: Choose databases like Cassandra for horizontal scaling in large applications.

• Evaluate consistency needs: Use strong consistency databases like MySQL for critical transaction...read more
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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.
Ans. 
Implement strategies like versioning, sharding, and caching to manage high I/O and reduce conflicts on the same document.
• Use versioning to track changes and allow concurrent edits without conflicts. For example, implement optimistic locking.

• Implement sharding to distribute the load across multiple servers, reducing the I/O on a single document.

• Utilize caching mechanisms to store frequently accessed data in memory, mini...read more
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Data Structures, Coding MCQs

Q1. What is Data Structure
Ans. 
Data structures are organized formats for storing, managing, and accessing data efficiently.
• 1. Types: Common data structures include arrays, linked lists, stacks, queues, trees, and graphs.

• 2. Arrays: Fixed-size collections of elements, e.g., [1, 2, 3, 4].

• 3. Linked Lists: Collections of nodes where each node points to the next, e.g., 1 -> 2 -> 3.

• 4. Stacks: Last-in, first-out (LIFO) structures, e.g., function call ...read more
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Q2. Write DFS Algorithm
Ans. 
Depth-First Search (DFS) is a graph traversal algorithm that explores as far as possible along each branch before backtracking.
• DFS uses a stack data structure, either explicitly or via recursion.

• It starts from a selected node and explores each branch before backtracking.

• Example: In a binary tree, DFS can be implemented using pre-order, in-order, or post-order traversal.

• DFS can be used to find connected components in a ...read more
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Easy level to Medium level

2 Easy questions of DSA

Q1. One DSA question
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Q2. Normal discussion about tech stack
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Q1. Tell about yourself
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Q2. Why do you want to join digit?
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Duration 1Hr
2 coding questions

Q1. Don't remember the questions
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Q2. Don't remember the questions.
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Q1. Dsa algorithm questions
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Q2. Sql questions queries
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