Square Software Engineer Interview Questions + Guide in 2025

Square is a global technology company focused on financial services, committed to building tools that help individuals and businesses access the economy effectively.

As a Software Engineer at Square, you will be part of a dynamic team responsible for developing and maintaining innovative software solutions that enhance the user experience across various platforms. Key responsibilities include designing, implementing, and supporting software applications, collaborating with cross-functional teams to define requirements, and ensuring optimal performance and security of the software systems. You will work on projects that span from initial concept to deployment, engaging with product management, design, and user experience teams to create scalable and efficient solutions.

A successful candidate will possess strong programming skills in languages such as Python, Java, or C++, along with a deep understanding of algorithms and data structures. Experience with system design, cloud computing, and API development is highly desirable. Additionally, a passion for solving complex problems, a collaborative mindset, and a commitment to continuous improvement are essential traits that align with Square's values of innovation and teamwork.

This guide will help you prepare for your interview by offering insights into the necessary skills and competencies, as well as potential questions you may encounter, giving you a strategic advantage in showcasing your qualifications.

The interview process for a Software Engineer at Square is designed to assess both technical skills and cultural fit within the company. It typically consists of several stages, each focusing on different aspects of the candidate's abilities and experiences.

1. Initial Recruiter Call

The process begins with a brief phone call with a recruiter. This conversation usually lasts about 30 minutes and serves as an opportunity for the recruiter to explain the role, the company culture, and the overall interview process. During this call, candidates are expected to discuss their background, skills, and motivations for applying to Square. The recruiter will also gauge the candidate's fit for the company and answer any preliminary questions.

2. Technical Screen

Following the initial call, candidates will participate in a technical screening, which is often conducted as a pair programming session. This interview typically lasts about an hour and focuses on coding skills. Candidates may be asked to solve algorithmic problems or work through coding challenges in real-time using platforms like CoderPad. The interviewer will assess the candidate's problem-solving approach, coding style, and ability to communicate their thought process.

3. Onsite Interview

The onsite interview is a more comprehensive evaluation that usually spans several hours and consists of multiple rounds. Candidates can expect to go through three to five technical interviews, which may include:

• Pair Programming Rounds: These sessions involve solving coding problems collaboratively with an interviewer. The problems are often designed to build on each other in complexity, allowing candidates to demonstrate their coding skills and adaptability.

• System Design Interview: In this round, candidates are tasked with designing a system or architecture for a specific application. Interviewers will look for a clear understanding of design principles, scalability, and the ability to articulate trade-offs in design decisions.

• Behavioral Interview: This portion focuses on the candidate's past experiences, teamwork, and how they align with Square's values. Candidates should be prepared to discuss their previous projects, challenges faced, and how they contributed to team success.

• Hiring Manager Interview: The final round often includes a conversation with the hiring manager, where candidates can ask questions about the team, projects, and expectations. This is also an opportunity for the manager to assess the candidate's fit within the team dynamics.

Throughout the interview process, candidates are encouraged to engage with their interviewers, ask questions, and demonstrate their enthusiasm for the role and the company.

As you prepare for your interview, it's essential to familiarize yourself with the types of questions that may be asked during each stage.

In this section, we’ll review the various interview questions that might be asked during a software engineering interview at Square. The interview process typically includes a mix of coding challenges, system design questions, and behavioral assessments. Candidates should be prepared to demonstrate their technical skills, problem-solving abilities, and collaborative mindset.

Coding and Algorithms

1. Can you explain how you would implement a function to sort an array of integers?

This question tests your understanding of sorting algorithms and their complexities.

How to Answer

Discuss the different sorting algorithms (like quicksort, mergesort, etc.) and their time complexities. Explain your choice of algorithm based on the problem constraints.

Example

“I would implement quicksort for its average-case time complexity of O(n log n). I would choose a pivot and partition the array into elements less than and greater than the pivot, then recursively sort the partitions.”

2. How would you find the longest substring without repeating characters?

This question assesses your ability to manipulate strings and use data structures effectively.

How to Answer

Outline a sliding window approach using a hash map to track characters and their indices.

Example

“I would use a hash map to store the last index of each character. As I iterate through the string, I would adjust the start of the substring whenever I encounter a repeating character, ensuring I always have the longest substring without duplicates.”

3. Describe how you would implement a cache in Python.

This question evaluates your understanding of caching mechanisms and data structures.

How to Answer

Discuss the use of dictionaries for O(1) access time and how you would handle cache eviction.

Example

“I would use a dictionary to store the cache entries and a linked list to keep track of the order of usage. When the cache exceeds its limit, I would evict the least recently used entry from both the dictionary and the linked list.”

4. Given a list of employees, write a function that pairs all employees.

This question tests your ability to work with data structures and algorithms.

How to Answer

Explain how you would use a loop to create pairs and ensure that each employee is only paired once.

Example

“I would iterate through the list and use a set to keep track of paired employees. For each employee, I would find another unpaired employee and create a pair, ensuring no one is paired more than once.”

5. How would you implement a function to validate a URL?

This question assesses your understanding of string manipulation and regular expressions.

How to Answer

Discuss the use of regular expressions to match valid URL patterns.

Example

“I would use a regular expression to check for the presence of a valid scheme, domain, and optional path. If the string matches the pattern, it’s a valid URL.”

System Design

1. Design a hotel reservation system.

This question evaluates your ability to design scalable systems.

How to Answer

Discuss the components of the system, including the database schema, APIs, and user interactions.

Example

“I would create a relational database with tables for hotels, rooms, and reservations. The API would allow users to search for available rooms, make reservations, and manage their bookings. I would also implement caching for frequently accessed data to improve performance.”

2. How would you design a scalable notification system?

This question tests your understanding of distributed systems and messaging queues.

How to Answer

Outline the use of message queues and how to handle different notification types.

Example

“I would use a message queue like RabbitMQ to handle notifications asynchronously. Each notification type would have its own consumer that processes messages and sends notifications via email, SMS, or push notifications.”

3. Describe how you would build a payment processing system.

This question assesses your knowledge of security and transaction management.

How to Answer

Discuss the importance of security, transaction integrity, and compliance with regulations.

Example

“I would implement a microservices architecture where each service handles a specific aspect of payment processing. I would ensure secure communication using HTTPS and implement logging and monitoring to track transactions and detect fraud.”

4. How would you approach designing a real-time chat application?

This question evaluates your understanding of real-time data transfer and user experience.

How to Answer

Discuss the use of WebSockets for real-time communication and how to handle message storage.

Example

“I would use WebSockets to enable real-time communication between clients. Messages would be stored in a database for retrieval, and I would implement user presence indicators to show who is online.”

5. Explain how you would design a system to handle user authentication and authorization.

This question tests your understanding of security best practices.

How to Answer

Discuss the use of tokens, OAuth, and secure password storage.

Example

“I would implement JWT tokens for stateless authentication and use OAuth for third-party integrations. Passwords would be hashed using bcrypt before storage to ensure security.”

Behavioral Questions

1. Tell me about a technical project you worked on that you are most familiar with.

This question assesses your ability to communicate your experiences and contributions.

How to Answer

Focus on your role, the challenges faced, and the impact of the project.

Example

“I led a team to develop a mobile application that streamlined the payment process for users. We faced challenges with integrating third-party APIs, but through collaboration and iterative testing, we successfully launched the app, which increased user engagement by 30%.”

2. How do you handle team conflict?

This question evaluates your interpersonal skills and conflict resolution strategies.

How to Answer

Discuss your approach to communication and finding common ground.

Example

“When conflicts arise, I believe in addressing them directly and openly. I encourage team members to express their viewpoints and work together to find a solution that aligns with our goals.”

3. Describe a time when you had to learn a new technology quickly.

This question assesses your adaptability and willingness to learn.

How to Answer

Share your learning process and how you applied the new technology.

Example

“I had to learn React quickly for a project. I dedicated time to online courses and built a small application to practice. This hands-on experience helped me become proficient enough to contribute effectively to the team.”

4. Why do you want to work at Square?

This question evaluates your motivation and alignment with the company’s values.

How to Answer

Discuss your admiration for the company’s mission and how your skills align with their goals.

Example

“I admire Square’s commitment to empowering businesses and individuals through innovative financial solutions. I believe my background in software engineering and passion for building impactful products align perfectly with Square’s mission.”

5. How do you prioritize your work when you have multiple deadlines?

This question assesses your time management and organizational skills.

How to Answer

Discuss your approach to prioritization and how you manage your workload.

Example

“I prioritize my tasks based on urgency and impact. I use tools like Trello to organize my work and regularly communicate with my team to ensure alignment on priorities.”