Juspay Technologies Backend Software Engineer Interview Questions and Answers

Detecting loop in a linked list

• Use two pointers, one moving one node at a time and the other moving two nodes at a time

• If there is a loop, the two pointers will eventually meet

• If any of the pointers reach the end of the list, there is no loop

DFS (Depth-First Search) is a graph traversal algorithm that explores as far as possible along each branch before backtracking.

• DFS uses a stack to keep track of visited nodes and explore adjacent nodes.

• It can be implemented recursively or iteratively.

• DFS is useful for solving problems like finding connected components, detecting cycles, and solving mazes.

To find a cycle in a graph, use depth-first search (DFS) and keep track of visited nodes.

• Implement DFS algorithm to traverse the graph

• Maintain a visited array to keep track of visited nodes

• If a visited node is encountered again during DFS, a cycle exists

Hashing is a process of converting data into a fixed-size numerical value called a hash code.

• Hashing is used to quickly retrieve data from large datasets.

• It is commonly used in data structures like hash tables and hash maps.

• Hash functions should be fast, deterministic, and produce unique hash codes for different inputs.

• Examples of hash functions include MD5, SHA-1, and SHA-256.

The question asks for the number of pairs between 1 and N that satisfy a specific mathematical relation.

• The relation is pow(a,3) + pow(b,3) = pow(c,3) + pow(d,3)

• The values of a, b, c, and d should be less than or equal to N

• Count the number of pairs that satisfy the relation

Merge sort is a divide-and-conquer algorithm that recursively divides an array into two halves, sorts them, and then merges them.

• Divide the array into two halves

• Recursively sort each half

• Merge the sorted halves back together

• Repeat until the entire array is sorted

I want to join PayPal because of its innovative technology, global impact, and strong company culture.

• Innovative technology - PayPal is known for its cutting-edge technology and digital payment solutions.

• Global impact - Working at PayPal would allow me to contribute to a company that has a worldwide reach and influence.

• Strong company culture - I value a company that prioritizes diversity, inclusion, and employee well-b...read more

I recently learned about the benefits of using Docker for containerization.

• Docker allows for easy packaging and deployment of applications

• It helps in creating consistent environments across different platforms

• Docker containers are lightweight and efficient

• Example: I used Docker to containerize a microservices architecture for a recent project

Find subset of numbers in array that sum up to zero.

• Use a nested loop to iterate through all possible subsets.

• Calculate the sum of each subset and check if it equals zero.

• Store the subset if the sum is zero.

• Optimize the solution by using a hash set to store the cumulative sum of elements.

BFS (Breadth-First Search) is a graph traversal algorithm that explores all the vertices of a graph in breadth-first order.

• BFS starts at a given vertex and explores all its neighbors before moving to the next level of vertices.

• It uses a queue data structure to keep track of the vertices to be visited.

• BFS guarantees that it visits all the vertices of a connected graph.

• It can be used to find the shortest path between two

In 5 years, I see myself as a highly skilled software developer, leading a team and contributing to innovative projects.

• Continuously improving my technical skills through learning and hands-on experience

• Taking on leadership roles and mentoring junior developers

• Contributing to the development of cutting-edge software solutions

• Building strong relationships with clients and stakeholders

• Staying updated with the latest indu...read more

My biggest achievement till date is successfully leading a team to develop and launch a new software product ahead of schedule.

• Led a team of developers to create a new software product

• Completed the project ahead of schedule

• Received positive feedback from clients and stakeholders

I would address conflicts directly and respectfully, seeking to understand the root cause and find a mutually beneficial solution.

• Listen actively to understand the other person's perspective

• Communicate clearly and respectfully

• Identify the root cause of the conflict

• Brainstorm potential solutions together

• Be willing to compromise and find a mutually beneficial solution

Success is achieving personal goals, feeling fulfilled, and making a positive impact.

• Success is subjective and can vary from person to person.

• It involves setting and achieving goals, both short-term and long-term.

• Feeling fulfilled and content with one's accomplishments is a key aspect of success.

• Making a positive impact on others or the world can also be a measure of success.

• Success is not just about material wealth or...read more

Dijkstra's algorithm finds the shortest path between nodes in a graph.

• Create a graph with nodes and edges

• Assign a tentative distance to each node

• Set the initial node as current and mark it visited

• For each neighbor of the current node, calculate the tentative distance

• If the tentative distance is less than the current distance, update the distance

• Mark the current node as visited and select the unvisited node with the sma...read more

A program to reverse a singly linked list

• Create a new empty linked list

• Traverse the original linked list and insert each node at the beginning of the new list

• Return the new list

Methods to find nth largest element in an unsorted linked list

• Traverse the linked list and store elements in an array, sort the array and return the nth largest element

• Use quickselect algorithm to find the nth largest element in O(n) time complexity

• Implement a max heap and extract the nth largest element

• Divide the linked list into smaller sublists and recursively find the nth largest element

• Use merge sort to sort the l

A prime number is a number that is divisible only by 1 and itself.

• A prime number has exactly two factors: 1 and itself.

• Prime numbers cannot be divided evenly by any other number.

• Examples of prime numbers include 2, 3, 5, 7, 11, 13, 17, etc.

Test cases for a bank transaction

• Transaction amount within account balance limit

• Transaction amount exceeds account balance limit

• Transaction to a valid account number

• Transaction to an invalid account number

• Transaction with correct transaction code

• Transaction with incorrect transaction code

• Transaction during bank working hours

• Transaction outside bank working hours

Design classes for educational institutions in a city

• Identify the main entities: schools, students, teachers, courses

• Create a School class with attributes like name, address, and a list of students and teachers

• Create a Student class with attributes like name, age, and a list of courses

• Create a Teacher class with attributes like name, specialization, and a list of courses

• Create a Course class with attributes like name, ...read more

Object Oriented Programming is a programming paradigm that uses objects to represent real-world entities.

• Encapsulation: bundling data and methods that operate on that data within one unit

• Inheritance: creating new classes from existing ones, inheriting their properties and methods

• Polymorphism: ability of objects to take on multiple forms or behaviors

• Abstraction: hiding complex implementation details and providing a simp...read more

Abstraction is hiding implementation details while polymorphism is using a single interface for multiple types.

• Abstraction: Encapsulation, Interfaces, Abstract classes

• Polymorphism: Method Overloading, Method Overriding, Interfaces

• Abstraction Example: Car - we don't need to know how the engine works to drive it

• Polymorphism Example: Animal - different animals have different sounds but they all have a 'makeSound' method

PayPal is an online payment system that allows individuals and businesses to transfer funds electronically.

• Allows users to make payments and money transfers online

• Offers a secure and convenient way to pay for goods and services

• Provides a platform for businesses to accept payments online

• Offers buyer and seller protection for eligible transactions

• Can be used to send and receive money internationally

I am excited to join PayPal because of its innovative culture and impact on the global economy.

• PayPal's commitment to innovation aligns with my passion for staying up-to-date with the latest technologies.

• I am impressed by PayPal's global reach and impact on the economy, and I want to be a part of that.

• I appreciate PayPal's focus on diversity and inclusion, and I believe in the importance of working for a company with s...read more