CoinDCX Backend Developer Interview Questions and Answers

A total time of 1 hour 30 minutes was given for this round, and it was held on the HackerEarth platform.

20 Aptitude questions- logical questions, questions on the diagram, time and train, direction, efficient statement, Venn diagram, few examples of the type of questions:

1. If 2 workers can paint 3 rooms in 4 hours, how many rooms can 1 worker paint in 5 hours

2. If there are 21 blue, 15 black and 17 red ball in a sack, how many minimum ball would you have to remove to ensure that you have removed at least 2 blue ball? (multiple questions of this type can be there)

3. The sum of the 5 numbers in AP is 80. The difference between each is 5. Smallest number?

4. A and B are standing in a row. A is 5th from the left, and B is 13th from the right. After they exchange their positions, A is 11th from left. How many people are in the row?

20 questions on CSE Fundamentals- Questions based on OS - Time Scheduling, Stacks, Find output and error in Java Code, Cpp code and C Code, DBMS, Time complexity, etc.

2 questions based on DSA, out of which you will have to attempt any 1.

For example, the Question was based on the array - in an abandoned city, you are given an array of gold coins, and you have to maximise the number of gold coins while moving in the city and traverse a minimum number of elements in the array.

Q1. 1. ARRAYS, STRINGS AND SORTING: Bubble sort, Complexity of all sorting algorithms.
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Q2. 2. Find the first non repeating character in a string
Ans. 
Find the first non-repeating character in a string.
• Create a hash table to store the frequency of each character in the string.

• Iterate through the string and check the frequency of each character.

• Return the first character with a frequency of 1.
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Q3. 3. Remove duplicates from an array
Ans. 
Remove duplicates from an array of strings
• Create a new empty array

• Loop through the original array and check if the element already exists in the new array

• If not, add it to the new array

• Return the new array
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Q4. 4. An array and 2 variables x and y are given, print y sub arrays with x elements.
Ans. 
Print y sub arrays with x elements from given array and variables.
• Use a loop to iterate through the array and create subarrays of x elements.

• Use another loop to print y number of subarrays.

• Handle edge cases where x or y is greater than the length of the array.
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Q5. 5. Explain the function pointer.
Ans. 
A function pointer is a variable that stores the memory address of a function.
• Function pointers allow passing functions as arguments to other functions.

• They can be used to implement callbacks and event handlers.

• Function pointers can be used to implement polymorphism in C.

• Example: int (*funcPtr)(int, int) = &add; where add is a function that takes two integers and returns their sum.

• Function pointers can also be used to
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Q6. 6. Explain copy constructor
Ans. 
Copy constructor creates a new object by copying an existing object.
• Used to initialize an object with another object of the same class

• Takes a reference to an object of the same class as a parameter

• Creates a new object with the same values as the parameter object

• Deep copy and shallow copy are two types of copy constructors
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Q7. 7. Deep copy / Shallow copy
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Q8. 8. Characteristics of static function
Ans. 
Static functions belong to the class and not to the instance of the class.
• Can be called without creating an instance of the class

• Cannot access non-static members of the class

• Can access other static members of the class

• Used for utility functions or helper functions
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Q9. 9. What are Abstract classes
Ans. 
Abstract classes are classes that cannot be instantiated and are meant to be extended by other classes.
• Abstract classes are declared using the 'abstract' keyword.

• They can have abstract and non-abstract methods.

• Abstract methods are declared without a body and must be implemented by the subclass.

• Abstract classes can have constructors and instance variables.

• They are useful for creating a common interface for a group of re
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Q1. 1. Explain Trees and Binary Search Trees.
Ans. 
Trees are data structures that store hierarchical data. Binary Search Trees are a type of tree that maintains sorted order.
• Trees are composed of nodes that have a parent-child relationship.

• Binary Search Trees have at most two children per node and the left child is always smaller than the parent while the right child is always larger.

• Binary Search Trees allow for efficient searching, insertion, and deletion operations.

• ...read more
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Q2. 2. Difference between Linked List and Tree (where what should be used).
Ans. 
Linked list is a linear data structure while tree is a hierarchical data structure.
• Linked list is used when we need to maintain a sequence of elements and perform operations like insertion and deletion at any position.

• Tree is used when we need to represent a hierarchical structure and perform operations like searching, insertion, and deletion efficiently.

• Linked list has a single pointer to the next node while tree has ...read more
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Q3. 3. A real-life example of Tree.
Ans. 
A family tree is a real-life example of a tree data structure.
• A family tree has a root node (the oldest ancestor) and branches out to children, grandchildren, etc.

• Each node can have multiple child nodes but only one parent node.

• The tree structure allows for easy visualization of relationships and ancestry.

• Other examples include file systems, organization charts, and decision trees.
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Q4. 4. Some in-depth questions from standard topics like Linked List, trees, etc. will also be asked.
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Q1. If a rival company tries to use your code against us what will you do?
Ans. 
I will ensure that our code is properly protected by implementing security measures and legal actions if necessary.
• Implement security measures such as encryption and access control to prevent unauthorized access to our code.

• Monitor for any suspicious activity and take immediate action if any unauthorized access is detected.

• If necessary, take legal action against the rival company for intellectual property theft.

• Collabo...read more
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Q1. Given 9 ball all of which weigh the same except for one, what is the minimum of weighings necessary to find the ball weighs more (or less)?
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Q1. 1. What are your goals for the next 1 year, your 5-year goals?
Ans. 
To become proficient in new technologies and frameworks, contribute to meaningful projects, and advance my career.
• Learn and master new programming languages, frameworks, and tools

• Contribute to open-source projects and collaborate with other developers

• Improve problem-solving and critical thinking skills

• Advance to a senior or lead developer role

• Stay updated with industry trends and best practices
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Q2. 2. What are the recent challenges you faced in life?
Ans. 
I recently faced the challenge of learning a new programming language and adapting to a new project.
• Learning a new programming language

• Adapting to a new project

• Working with unfamiliar technologies

• Meeting tight deadlines
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Q3. 3. What are your hobbies in life besides coding?
Ans. 
I enjoy playing musical instruments, reading books, and hiking in my free time.
• Playing musical instruments

• Reading books

• Hiking
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Q4. 4. Why do you want to join this company?
Ans. 
I want to join this company because of its strong reputation in the industry and its commitment to innovation.
• Strong reputation in the industry

• Commitment to innovation

• Opportunity for professional growth

• Positive work culture

• Exciting projects and challenges
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Q5. 5. What work does our company do?
Ans. 
Our company provides backend development services for various industries.
• We develop and maintain backend systems for clients

• We specialize in creating scalable and efficient APIs

• Our work involves database management and optimization

• We collaborate with frontend developers to ensure seamless integration

• We follow industry best practices and stay updated with the latest technologies
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