Celebal Technologies Javascript Developer Interview Questions and Answers

Game based Aptitude test

Multiple choice questions on OPPS and pseudo codes with 2 questions on java and 2 on sql

Q1. Java collections
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Q2. Exception Handling
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Q3. Some tricky programs output
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Q1. Personal Inquiry
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Q2. Location confirmation
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Q1. Find longest palindromic substring in a given string.
Ans. 
Use dynamic programming to find the longest palindromic substring in a given string.
• Iterate through the string and expand around each character to find palindromes.

• Store the length of the longest palindrome found so far.

• Return the substring based on the start and end indices of the longest palindrome.
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Q2. How to serialize and deserialise a tree
Ans. 
To serialize and deserialize a tree, use a recursive approach to traverse the tree and store the data in a suitable format.
• Use pre-order traversal to serialize the tree by storing the node values in a list or string.

• For deserialization, reconstruct the tree by recursively building nodes from the serialized data.

• Consider using JSON or XML format for serialization to easily store and retrieve tree structure.
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Q3. Find if a given regex (containing ., * and lower case english chars) matches a given string.
Ans. 
Use regex library to match given regex with string.
• Use a regex library like re in Python to match the given regex with the string.

• Check if the regex matches the string using the library functions.

• Handle cases where the regex contains special characters like . and * appropriately.
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Q4. Explain about throttling and implement throttle function.
Ans. 
Throttling is a technique used to control the rate of requests sent to a server.
• Throttling helps prevent server overload by limiting the number of requests processed at a time.

• Implementing a throttle function involves setting a maximum request rate and delaying excess requests.

• Example: Implementing a throttle function in a web application to limit the number of API calls made to a third-party service.

• Example: Throttlin...read more
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Q1. Find squares of elements in a sorted array and return the sorted response.
Ans. 
Sort the squares of elements in a sorted array and return the sorted response.
• Iterate through the array and square each element.

• Store the squared values in a new array.

• Sort the new array and return it.
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Q2. Write a short promise example and implement your own promise
Ans. 
A promise is a commitment to do something in the future, typically used for asynchronous operations in JavaScript.
• Promises are used to handle asynchronous operations in JavaScript.

• They represent a value that may be available now, in the future, or never.

• Promises have three states: pending, fulfilled, or rejected.

• Example: new Promise((resolve, reject) => { setTimeout(() => resolve('Done!'), 1000); });
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Q3. Explain event loop, what are different types of queues in event loop
Ans. 
Event loop is a mechanism that allows for asynchronous execution of code by managing the order of events in a single thread.
• Event loop continuously checks the call stack for any functions that need to be executed, and processes them in a non-blocking manner.

• Different types of queues in event loop include microtask queue (Promise callbacks), macrotask queue (setTimeout, setInterval callbacks), and animation frame queue
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Q4. What is virtual DOM and why its faster
Ans. 
Virtual DOM is a lightweight copy of the actual DOM, used to improve performance by minimizing direct manipulation of the real DOM.
• Virtual DOM is a concept used in frameworks like React to optimize rendering performance.

• Changes are first made to the virtual DOM, which is then compared to the real DOM to identify the minimal updates needed.

• This approach reduces the number of actual DOM manipulations, resulting in faster...read more
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Q1. Discuss the project you are most proud of
Ans. 
Developed a mobile app for tracking personal fitness goals
• Used React Native to create a cross-platform app

• Implemented features such as goal setting, progress tracking, and workout logging

• Integrated with wearable devices like Fitbit for automatic data syncing
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Q2. What are ways to speed up SQL queries? List them in increasing order of complexity?
Ans. 
Ways to speed up SQL queries in increasing order of complexity
• Use indexes on columns frequently used in WHERE clauses

• Optimize queries by avoiding unnecessary joins and subqueries

• Use stored procedures to reduce network traffic and improve performance

• Consider denormalizing tables for frequently accessed data

• Use query optimization techniques like query caching and query hints
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Q3. Is Redis single-threaded or multi-threaded?
Ans. 
Redis is single-threaded.
• Redis is single-threaded, meaning it can only execute one command at a time.

• This design choice allows Redis to be extremely fast and efficient for certain use cases.

• However, it also means that Redis may not be the best choice for highly concurrent workloads.
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Q4. What sort of data types can be used as keys in Python?
Ans. 
Data types that can be used as keys in Python include strings, integers, floats, tuples, and custom objects.
• Strings are commonly used as keys in Python dictionaries.

• Integers and floats can also be used as keys.

• Tuples can be used as keys if they only contain immutable elements.

• Custom objects can be used as keys if they are hashable.

• Examples: {'name': 'John'}, {1: 'apple'}, {(1, 2): 'tuple'}
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Q5. What types of indexing exist in SQL?
Ans. 
Types of indexing in SQL include clustered, non-clustered, unique, and composite indexes.
• Clustered index physically reorders the table based on the index key

• Non-clustered index creates a separate structure for the index

• Unique index ensures that all values in the index column are unique

• Composite index uses multiple columns for indexing
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Q1. Basic java fundamentals
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Q2. Spring boot,sql
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Q1. Some technical questions from manager
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Q2. Some challenges or scenario based questions
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Q1. Salary discussion mostly
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Q2. Benifts that they offer with TR
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Q1. What is the importance of manual testing when compared to automation testing
Ans. 
Manual testing is important for exploratory testing, usability testing, and ad-hoc testing.
• Manual testing allows for exploratory testing where testers can explore the application and identify unexpected issues.

• Usability testing, which involves real users interacting with the software, is best done manually to capture user experience.

• Ad-hoc testing, where testers randomly test the application without predefined test cas...read more
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Q2. Real life scenario on web application testing
Ans. 
Testing a web application for an online shopping platform
• Testing the functionality of adding items to the cart and checking out

• Testing the payment gateway integration for secure transactions

• Testing the search functionality to ensure accurate results are displayed

• Testing the responsiveness of the website on different devices and browsers
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Q1. What is the inheritance?
Ans. 
Inheritance is a mechanism in object-oriented programming where a class inherits properties and behaviors from another class.
• Allows a class to inherit attributes and methods from another class

• Promotes code reusability and reduces redundancy

• Creates a parent-child relationship between classes

• Derived class can override or extend the functionality of the base class
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Q2. What are the types of joins in mysql
Ans. 
Types of joins in MySQL include inner join, left join, right join, and full join.
• Inner join: Returns rows when there is a match in both tables.

• Left join: Returns all rows from the left table and the matched rows from the right table.

• Right join: Returns all rows from the right table and the matched rows from the left table.

• Full join: Returns rows when there is a match in one of the tables.
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Q1. How to handle multiple api's
Ans. 
Use a centralized API gateway to manage and route requests to multiple APIs efficiently.
• Implement a centralized API gateway to handle incoming requests and route them to the appropriate API based on the endpoint.

• Utilize API management tools like Apigee, Kong, or AWS API Gateway to manage and monitor multiple APIs.

• Consider implementing a caching layer to improve performance and reduce the number of requests to external
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Q2. What does strstr function do?
Ans. 
strstr function searches for a substring within a string and returns a pointer to the first occurrence of the substring.
• Used in C programming language

• Syntax: char *strstr(const char *haystack, const char *needle)

• Example: char *str = strstr("hello world", "world")
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Maths ,english ,reasoning, puzzles

Jackeron was the platform

Q1. Design zepto delivery system .
Ans. 
Design a zepto delivery system for efficient and fast delivery of small packages.
• Utilize drones for quick and efficient delivery

• Implement a centralized hub for package sorting and distribution

• Use GPS tracking for real-time package monitoring

• Optimize routes for faster delivery times

• Ensure secure and reliable delivery process
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