Visa Senior Systems Engineer Interview Questions, Process, and Tips

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

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

Implementing a shuffle function for a playlist of songs

• Create a new empty playlist

• Randomly select a song from the original playlist and add it to the new playlist

• Remove the selected song from the original playlist

• Repeat until all songs have been added to the new playlist

• Return the new shuffled playlist

Memory leak is a situation where a program fails to release memory it no longer needs.

• Memory leaks can cause a program to consume more and more memory over time, eventually leading to crashes or other issues.

• Memory leaks can be caused by programming errors such as not freeing memory after it is no longer needed.

• Tools like valgrind can be used to detect memory leaks in C and C++ programs.

• Examples of memory leaks include...read more

Arrays have fixed size and can lead to memory wastage and performance issues.

• Arrays have a fixed size and cannot be resized dynamically.

• Inserting or deleting elements in an array can be time-consuming.

• Arrays can lead to memory wastage if they are not fully utilized.

• Arrays can cause performance issues if they are too large and need to be traversed frequently.

• Arrays can also be prone to buffer overflow attacks.

• Example: A...read more

Function to hide text on mouse click in JavaScript

• Create a function that takes an element as input

• Add an event listener to the element for a mouse click

• Toggle the element's display property between 'none' and its original value

Find two elements in an unsorted array whose sum is equal to a given number x.

• Use a hash table to store the difference between x and each element in the array.

• Iterate through the array and check if the current element is in the hash table.

• Return the pair of elements that add up to x.

BST stands for Binary Search Tree, a data structure used for efficient searching and sorting operations.

• BST is a tree-like data structure where each node has at most two children.

• The left child of a node contains a value less than the parent node, while the right child contains a value greater than the parent node.

• BST allows for efficient searching and sorting operations with a time complexity of O(log n).

• Examples of a...read more

Number of possible BSTs with 2 and 3 nodes.

• For 2 nodes, only 2 BSTs are possible.

• For 3 nodes, 5 BSTs are possible.

• Number of BSTs can be calculated using Catalan numbers formula.

• Catalan(2) = 2, Catalan(3) = 5.

Answering the question about possible trees with two and three nodes.

• For two nodes, there is only one possible tree.

• For three nodes, there are three possible trees.

• The formula for calculating the number of possible trees with n nodes is (2n-3)!!.

• The double exclamation mark represents the double factorial function.

• The double factorial function is defined as n!! = n(n-2)(n-4)...(1 or 2).

B+ trees are balanced trees used for indexing and searching large amounts of data.

• B+ trees are similar to binary search trees but have multiple keys per node.

• They are commonly used in databases and file systems.

• B+ trees have a high fanout, reducing the number of disk accesses required for searching.

• They are also self-balancing, ensuring efficient performance even with large amounts of data.

• Example: In a database, a B+ ...read more

Yes, I have a few questions.

• Can you tell me more about the team I'll be working with?

• What is the company culture like?

• What are the biggest challenges the team is currently facing?

• Can you walk me through the development process for a typical project?

• What opportunities are there for professional growth and development?

I prefer hash tables for their constant time lookup and insertion.

• Hash tables are efficient for storing and retrieving data.

• They have constant time complexity for both insertion and lookup.

• They can be implemented using arrays or linked lists.

• Examples include Python's dictionary and Java's HashMap.

Yes, we can implement a stack using two queues.

• Push operation: Enqueue the element to the first queue.

• Pop operation: Dequeue all elements from the first queue and enqueue them to the second queue until the last element. Dequeue and return the last element. Swap the names of the queues.

• Top operation: Same as pop operation but don't dequeue the last element.

• Example: Push 1, 2, 3. Queue 1: 1 2 3. Queue 2: empty. Pop opera...read more

Find minimum no of platforms required to avoid collision between trains based on their arrival and departure times.

• Sort both arrays in ascending order

• Initialize platform count and max count to 1

• Loop through both arrays and compare arrival and departure times

• If arrival time is less than or equal to departure time, increment platform count

• Else, decrement platform count

• Update max count if platform count is greater than ma

JVM stands for Java Virtual Machine. It is an abstract machine that provides a runtime environment for Java programs.

• JVM is responsible for interpreting the compiled Java code and executing it.

• It provides platform independence by converting bytecode into machine-specific code.

• JVM has various components like class loader, bytecode verifier, and execution engine.

• Compiler converts source code into bytecode, while JVM exec...read more

I am a software engineer with experience in developing web applications and a passion for learning new technologies.

• Experienced in developing web applications using technologies such as Java, Spring, and Angular

• Passionate about learning new technologies and keeping up with industry trends

• Strong problem-solving skills and ability to work in a team environment

• Completed a Bachelor's degree in Computer Science from XYZ Uni

PayTM is an Indian e-commerce payment system and digital wallet company.

• PayTM was founded in 2010 by Vijay Shekhar Sharma.

• It started as a mobile recharge and bill payment platform.

• PayTM has expanded to offer services like online shopping, movie ticket booking, and travel bookings.

• It also offers a digital wallet that can be used to pay for various services and products.

• PayTM has over 350 million registered users and is ...read more

I would like to add a feature for splitting bills among friends.

• The feature would allow users to split bills for movies, dinners, etc.

• Users can select friends from their contact list and split the bill equally or unequally.

• The app would send a notification to the selected friends to pay their share.

• The feature would make it easier for users to split expenses and avoid awkward conversations.

• It would also encourage more

My favourite app is Spotify. I would like to see improvements in the algorithm for personalized playlists.

• Improved algorithm for personalized playlists

• Better integration with social media platforms

• Option to create collaborative playlists with friends

My favourite subject is Computer Science.

• I enjoy programming and problem-solving.

• I find algorithms and data structures fascinating.

• I am interested in artificial intelligence and machine learning.

• I like learning about new technologies and keeping up with industry trends.

I choose NIT Hamirpur because of its excellent academic reputation and beautiful campus.

• NIT Hamirpur has a strong focus on academics and research, which aligns with my career goals.

• The campus is located in a serene and picturesque location, which provides a conducive environment for learning.

• The faculty members are highly experienced and knowledgeable, and are always willing to help students.

• The college has state-of-th...read more

Count the number of continuous sequences with equal number of 0's and 1's in an array.

• Iterate through the array and keep track of the count of 0's and 1's encountered so far.

• Store the difference between the counts in a hash table and increment the count for that difference.

• If the difference is already present in the hash table, add the count to the existing value.

• Return the sum of all values in the hash table.

Count the number of palindromic substrings in a given string.

• A substring is a contiguous sequence of characters within a string.

• A palindrome is a string that reads the same backward as forward.

• Use dynamic programming to count all palindromic substrings.

• Time complexity can be reduced to O(n^2) using Manacher's algorithm.

Find the longest palindrome in a given string in linear time complexity.

• Use Manacher's algorithm to find the longest palindrome in a string in O(n) time complexity.

• The algorithm involves preprocessing the string to add special characters to handle even and odd length palindromes.

• Then, it uses a combination of dynamic programming and symmetry properties to find the longest palindrome.

• For example, in the string 'babad',

The value of pie is a mathematical constant approximately equal to 3.14159.

• Pie is the ratio of the circumference of a circle to its diameter.

• It is an irrational number, meaning it cannot be expressed as a finite decimal or fraction.

• Pie is commonly used in geometry and trigonometry calculations.

• The value of pie is often approximated as 3.14 or 22/7.

I am a passionate software engineer with experience in developing web applications using various technologies.

• Experienced in developing web applications using HTML, CSS, JavaScript, and frameworks like React and Angular

• Proficient in backend development with Node.js and databases like MongoDB and MySQL

• Familiar with version control systems like Git and deployment tools like Docker

• Strong problem-solving skills and ability

Yes, I believe I will be able to fit in the company based on my experience, skills, and values.

• I have experience working in diverse teams and adapting to different work cultures.

• I share the company's values and vision, which align with my own.

• I am eager to learn and contribute to the team, fostering a positive work environment.

• I have strong communication skills, which are essential for collaboration and teamwork.