PubMatic Software Engineer Interview Questions + Guide in 2025

PubMatic is an independent technology company focused on maximizing customer value by delivering innovative solutions in the digital advertising supply chain.

As a Software Engineer at PubMatic, you will be responsible for designing, developing, and implementing highly scalable and fault-tolerant applications that process terabytes of data. This role will involve working with modern technology stacks, including but not limited to Java, Spark, Hadoop, Kafka, and various data storage solutions. You will collaborate closely with cross-functional teams to deliver end-to-end products and features, while also customizing applications based on customer requirements. A strong understanding of data structures, algorithms, and systems programming is critical, as well as experience in Agile methodologies. You should also be prepared to engage in code and design reviews, ensuring high-quality software delivery.

This guide will help you prepare for technical interviews by focusing on the key areas PubMatic values, including problem-solving skills, system design, and proficiency in programming languages relevant to the role.

In this section, we’ll review the various interview questions that might be asked during a Software Engineer interview at PubMatic. The interview process will likely assess your technical skills, problem-solving abilities, and understanding of software engineering principles, particularly in the context of big data and scalable systems. Be prepared to demonstrate your knowledge of data structures, algorithms, and system design, as well as your proficiency in programming languages such as Java and C++.

Data Structures and Algorithms

1. Can you explain the difference between a stack and a queue?

Understanding the fundamental data structures is crucial for any software engineering role.

How to Answer

Discuss the definitions of both data structures, their use cases, and how they operate (LIFO for stacks and FIFO for queues).

Example

“A stack is a data structure that follows the Last In First Out (LIFO) principle, meaning the last element added is the first to be removed. It’s commonly used in scenarios like function call management in programming. A queue, on the other hand, follows the First In First Out (FIFO) principle, where the first element added is the first to be removed, making it ideal for scenarios like task scheduling.”

2. How would you reverse a linked list?

This question tests your understanding of linked lists and manipulation techniques.

How to Answer

Explain the iterative and recursive approaches to reversing a linked list, highlighting the time and space complexity of each.

Example

“To reverse a linked list iteratively, I would maintain three pointers: previous, current, and next. I would iterate through the list, adjusting the pointers to reverse the links. The recursive approach involves reversing the rest of the list and adjusting the pointers accordingly. Both methods have a time complexity of O(n) and a space complexity of O(1) for the iterative approach and O(n) for the recursive approach due to the call stack.”

3. Describe how you would implement a binary search algorithm.

Binary search is a fundamental algorithm that demonstrates your understanding of searching techniques.

How to Answer

Outline the steps of the binary search algorithm and its requirements, such as the need for a sorted array.

Example

“Binary search works by repeatedly dividing the search interval in half. If the target value is less than the middle element, the search continues in the lower half; otherwise, it continues in the upper half. This process continues until the target value is found or the interval is empty. The time complexity is O(log n), making it efficient for large datasets.”

4. What is a hash table, and how does it work?

This question assesses your knowledge of hash-based data structures.

How to Answer

Explain the concept of hash tables, including how they store key-value pairs and handle collisions.

Example

“A hash table is a data structure that maps keys to values for efficient data retrieval. It uses a hash function to compute an index into an array of buckets or slots, from which the desired value can be found. Collisions, where two keys hash to the same index, can be handled using techniques like chaining or open addressing.”

5. Can you explain the concept of dynamic programming?

Dynamic programming is a key algorithmic technique that can optimize recursive solutions.

How to Answer

Discuss the principles of dynamic programming, including overlapping subproblems and optimal substructure.

Example

“Dynamic programming is an optimization technique used to solve problems by breaking them down into simpler subproblems and storing the results of these subproblems to avoid redundant calculations. For example, in the Fibonacci sequence, instead of recalculating the same values multiple times, we can store them in an array and retrieve them as needed, significantly improving efficiency.”

System Design

1. How would you design a URL shortening service?

This question tests your ability to design scalable systems.

How to Answer

Outline the components of the system, including the database schema, API endpoints, and considerations for scalability and performance.

Example

“To design a URL shortening service, I would create a database with a table for storing original URLs and their corresponding shortened versions. The API would include endpoints for creating a short URL and redirecting to the original URL. For scalability, I would implement caching for frequently accessed URLs and use a distributed database to handle high traffic.”

2. Describe how you would implement a real-time analytics system.

This question assesses your understanding of big data technologies and real-time processing.

How to Answer

Discuss the architecture of the system, including data ingestion, processing, and storage components.

Example

“I would implement a real-time analytics system using a combination of Apache Kafka for data ingestion, Apache Spark for processing, and a NoSQL database like Cassandra for storage. The system would allow for real-time data processing and analytics, enabling users to query and visualize data as it arrives.”

3. What considerations would you take into account when designing a fault-tolerant system?

This question evaluates your understanding of system reliability and availability.

How to Answer

Discuss redundancy, data replication, and failover strategies.

Example

“When designing a fault-tolerant system, I would ensure redundancy by deploying multiple instances of services across different availability zones. Data replication would be implemented to ensure data integrity, and I would establish failover mechanisms to switch to backup systems in case of failure, ensuring minimal downtime.”

4. How would you approach designing a distributed caching system?

This question tests your knowledge of caching strategies and distributed systems.

How to Answer

Explain the principles of caching, including cache invalidation and consistency.

Example

“To design a distributed caching system, I would use a key-value store like Redis or Memcached. I would implement strategies for cache invalidation, such as time-to-live (TTL) and write-through caching, to ensure data consistency. Additionally, I would consider partitioning the cache to distribute load and improve performance.”

5. Can you explain the CAP theorem?

This question assesses your understanding of distributed systems.

How to Answer

Discuss the three components of the CAP theorem: Consistency, Availability, and Partition Tolerance.

Example

“The CAP theorem states that in a distributed data store, it is impossible to simultaneously guarantee all three of the following: Consistency (all nodes see the same data at the same time), Availability (every request receives a response), and Partition Tolerance (the system continues to operate despite network partitions). In practice, systems must make trade-offs between these components based on their specific requirements.”

Here are some tips to help you excel in your interview.

Understand the Interview Structure

The interview process at PubMatic typically consists of multiple rounds, including technical, design, and managerial interviews. Familiarize yourself with this structure and prepare accordingly. Expect a technical round focused on coding and algorithms, a low-level design (LLD) round, and a managerial round that will assess your behavioral skills. Knowing what to expect will help you manage your time and energy effectively during the interview.

Master Core Technical Skills

Given the emphasis on coding and algorithms, ensure you have a strong grasp of data structures, algorithms, and system design principles. Brush up on Java, as it is a key language for the role. Practice coding problems that range from basic to advanced levels, particularly those involving linked lists, arrays, and tree manipulations. Familiarize yourself with common design patterns and be prepared to discuss your thought process while solving problems.

Prepare for System Design Questions

The LLD round can be challenging if you haven't prepared adequately. Review system design concepts and be ready to discuss how you would approach designing scalable and fault-tolerant systems. Think about how to break down complex problems into manageable components and articulate your design choices clearly. Practice explaining your designs to a peer or mentor to gain confidence.

Emphasize Problem-Solving and Communication Skills

During the interviews, you will be evaluated not just on your technical skills but also on your problem-solving approach and communication abilities. Be prepared to explain your reasoning and thought process as you work through coding problems. If you get stuck, don’t hesitate to ask clarifying questions or discuss your thought process with the interviewer. This shows your collaborative spirit and willingness to learn.

Showcase Your Experience with Big Data Technologies

Given the focus on big data platforms at PubMatic, highlight any experience you have with technologies such as Spark, Hadoop, Kafka, and others mentioned in the job description. Be ready to discuss specific projects where you utilized these technologies, the challenges you faced, and how you overcame them. This will demonstrate your hands-on experience and understanding of the tools relevant to the role.

Be Ready for Behavioral Questions

The managerial round will likely include behavioral questions. Prepare to discuss your past experiences, focusing on teamwork, conflict resolution, and project management. Use the STAR (Situation, Task, Action, Result) method to structure your responses, ensuring you convey your contributions and the impact of your actions clearly.

Align with Company Culture

PubMatic values collaboration, innovation, and a strong work ethic. Research the company culture and think about how your values align with theirs. Be prepared to discuss why you want to work at PubMatic and how you can contribute to their mission. Showing that you understand and resonate with their culture can set you apart from other candidates.

Follow Up and Stay Engaged

After your interviews, consider sending a thank-you email to express your appreciation for the opportunity and reiterate your interest in the role. This not only shows professionalism but also keeps you on the interviewers' radar.

By following these tips and preparing thoroughly, you will position yourself as a strong candidate for the Software Engineer role at PubMatic. Good luck!

The interview process for a Software Engineer at PubMatic is structured and thorough, designed to assess both technical and interpersonal skills. It typically consists of several rounds, each focusing on different aspects of the candidate's abilities.

1. Initial Screening

The process begins with an initial screening, which may be conducted by a recruiter or a hiring manager. This round usually involves a discussion about your background, experience, and motivation for applying to PubMatic. The recruiter will also provide insights into the company culture and the specifics of the role.

2. Technical Assessment

Following the initial screening, candidates typically undergo a technical assessment. This may include an online coding test that evaluates your proficiency in programming languages such as Java, C++, or Python, as well as your understanding of data structures and algorithms. The assessment often consists of multiple-choice questions and coding challenges that test your problem-solving skills in real-time.

3. Technical Interviews

Candidates who perform well in the technical assessment are invited to participate in one or more technical interviews. These interviews are usually conducted by senior engineers or technical leads and focus on in-depth discussions about your coding skills, system design, and understanding of software engineering principles. Expect to solve coding problems on a whiteboard or through a shared coding platform, with questions ranging from basic algorithms to complex system design scenarios.

4. Managerial Round

After the technical interviews, candidates may have a managerial round. This round typically focuses on behavioral questions and assesses your fit within the team and the company culture. Interviewers may ask about your previous experiences, how you handle challenges, and your approach to teamwork and collaboration. This is also an opportunity for you to ask questions about the team dynamics and the projects you would be working on.

5. HR Interview

The final step in the interview process is usually an HR interview. This round covers logistical aspects such as salary expectations, availability, and other administrative details. It may also include questions about your long-term career goals and how they align with the opportunities at PubMatic.

Throughout the interview process, candidates are encouraged to demonstrate their technical expertise, problem-solving abilities, and collaborative mindset.

Next, let's explore the specific interview questions that candidates have encountered during their interviews at PubMatic.

1. Write a program to determine the term frequency (TF) values for each term in a document.

Given a text document in the form of a string, write a program to determine the term frequency (TF) values for each term in the document. Round the term frequency to 2 decimal points.

2. Create a function get_ngrams to return a dictionary of n-grams and their frequency in a string.

Write a function get_ngrams to take in a word (string) and return a dictionary of n-grams and their frequency in the given string.

3. Write a function to return the sum of the elements in a matrix.

Given a matrix of integers, write a function that returns the sum of the elements in the matrix. The function should handle both positive and negative integers and return the sum as an integer.

4. Write a function to find the nearest common ancestor of two nodes in a binary tree.

Given a binary tree of unique positive numbers and two nodes as input, write a function to return the value of the nearest node that is a parent to both nodes. If one of the nodes doesn’t exist in the tree, return -1.

5. Write a function to add together all combinations of adjacent integers in a string.

Write a Python function that adds together all combinations of adjacent integers of a given string of integers named int_str.

6. How would you explain what a p-value is to someone who is not technical?

Explain the concept of a p-value in simple terms to a non-technical person, focusing on its role in determining the significance of results in experiments or studies.

7. What could be the cause of the decrease in overall capital approval rates?

Analyze why the overall capital approval rate dropped from 85% to 82% despite individual product approval rates staying flat or increasing. Consider factors like changes in the mix of products or external influences.

8. What is the probability that both flips result in the same side with one fair and one biased coin?

Calculate the probability that two flips of a randomly selected coin (one fair, one biased with ³⁄₄ heads) result in the same side.

9. What is the percentage chance a review is actually fake when the algorithm detects it as fake?

Given that 98% of reviews are legitimate and 2% are fake, and the algorithm’s accuracy rates, calculate the probability that a review is fake when identified as such by the algorithm.

10. What kind of analysis would you run for non-normal distribution in an AB test with low data at Uber Fleet?

Determine the appropriate analysis method for an AB test with non-normal distribution and low data volume at Uber Fleet, and explain how to measure which variant won.

11. What are the assumptions of linear regression?

List and explain the key assumptions that must be met for linear regression analysis to be valid.

12. How would you set up an A/B test for multiple changes in a sign-up funnel?

A team wants to A/B test changes like button color (red to blue) and position (top to bottom) to increase click-through rates. How would you design this test?

13. Where and how could you promote Instagram through Facebook?

You work on Facebook’s growth team and need to promote Instagram within the Facebook app. Where and how would you implement this promotion?

14. What metrics/graphs/models would you use to analyze churn behavior for different pricing plans?

Netflix has two pricing plans: $15/month and $100/year. An executive wants an analysis of churn behavior for these plans. What metrics, graphs, or models would you use to provide an overview of subscription performance?

15. How would you analyze an A/B test with non-normal distribution for Uber Fleet?

Uber Fleet has low data for experimentation, and an A/B test shows a non-normal distribution. What kind of analysis would you run, and how would you determine which variant won?

16. What retention rate is needed to surpass revenue from a non-subscription price?

You sell an e-commerce product for $29 with a 50% margin. You want to offer a monthly subscription at a 20% discount. What retention rate is required to surpass the revenue from the non-subscription price?

You should plan to brush up on any technical skills and try as many practice interview questions and mock interviews as possible. A few tips for acing your PubMatic Software Engineer interview include:

• Prepare for All Levels of Coding Questions: The technical interviews can range from basic to advanced levels. Be sure to practice coding questions extensively, focusing on data structures, algorithms, and problem-solving.
• Bring Your A-Game in Design Questions: Low-level design questions can be challenging if you’re not well-practiced. Brush up on system design principles and be ready to explain your thought process comprehensively.
• Showcase Your Behavioral Excellence: The HR and managerial rounds are crucial for demonstrating your soft skills and cultural fit. Be prepared to discuss your past experiences, challenges, and how you solved them.

What is the average salary for a Software Engineer at PubMatic?

According to Glassdoor, Software Engineers at PubMatic earn between $113K to $163K per year, with an average of $135K per year.

How long does the entire interview process take?

The timeline can vary depending on the candidate’s progress through each round and the company’s hiring schedule. Generally, the process may include an initial test, followed by 2-3 technical interviews, and a final HR round, making it a thorough evaluation.

What is the company culture at PubMatic like?

PubMatic boasts a collaborative and innovative work environment. Regular communication with HR and technical interviewers is highlighted as positive, and the company supports diversity and inclusion while offering various benefits such as stock options, healthcare, and flexible work schedules.

The interview process at PubMatic for the Software Engineer position is rigorous. Candidates can expect multiple technical rounds that feature coding challenges, data structures and algorithms, system design questions, and behavioral interviews.

To ace your interview at PubMatic, preparation is vital. Familiarize yourself with common interview questions that range from core Java, system design challenges, to data structures and algorithms. Dive deep into the company’s interview process and list of possible questions with our main PubMatic Interview Guide, which offers a comprehensive look at what to expect and how to prepare.

Good luck with your interview!