Square Software Engineer Interview Guide

The first round of the Square Software Engineer Interview (or if you'd prefer - Block Software Engineer interview) is a brief screening call that typically lasts between 15-20 minutes. This is an informal conversation where a recruiter will reach out to you after you have applied for the position through LinkedIn or another platform.

The recruiter will ask you some basic questions about your previous work experience, organizations you have worked with, your skillset, and your compensation details. 

If your profile matches what the company is looking for, you will be invited to move forward with the technical phone screen interview.

The technical or coding phone screen is typically conducted remotely over Zoom and is designed to evaluate your proficiency in data structures and algorithms through one or two coding problems. You might also want to explore the similar hiring processes for Software Engineer roles at Meta and Google.

The coding problems presented are generally not the same as the ones found on typical coding platforms like LeetCode or HackerRank; they are related to real-world scenarios, and you will be required to write code that solves the problem optimally.

Here are a few example questions:

• Write an efficient algorithm to find the shortest driving distance between two locations on a map.
• Write an algorithm to identify fraudulent transactions in a large dataset based on criteria such as the transaction amount, time of day, location, and purchase history of the cardholder.

If you perform well during the technical screen, you will be invited for an on-site interview to further evaluate your skills and fit.

Like the technical screen, Square's on-site interview is conducted over Zoom and comprises the following interviews:

• Technical Interviews
• Behavioral Interview 

Technical Interview

The technical interview includes a bunch of pair programming interviews, technical Q&A sessions, and system design interviews with senior developers. These interviews are designed to test your knowledge of programming concepts and your ability to solve real-world problems.

Let's discuss the pair programming interviews first which set Square apart from other companies. 

Pair Programming Interview

In the pair programming interviews, you will need to collaborate with the interviewer to solve practical design-oriented problems using common data structures. Unlike a phone Coderpad interview, you will have access to resources such as Google and IDEs. 

The problems presented are typically related to real-world scenarios, rather than abstract leetcode-style/HackerRank questions.

You can bounce ideas off of your "pair" (the interviewer) to hack up a working code and test cases while demonstrating your ability to break down a problem, use libraries and test frameworks, and collaborate effectively. 

Make sure you have a good grasp of various concepts in algorithms, including sorting algorithms, OO fundamentals, parsing, recursion, arrays, linked lists, trees, and graphs. 

Here are six example questions for a pair programming interview:

• Given a list of integers, write a function to return the two numbers that add up to a given target value. You can assume that there is only one solution, and that each element in the list is unique.
• Write a function to determine if a binary tree is a binary search tree (BST). A binary search tree is a tree in which every node's value is greater than all the values in the left subtree and less than all the values in the right subtree.
• Write a function to generate a Fibonacci sequence up to a given number. Provide a minimal solution that has a time complexity of O(n) and uses O(1) space complexity.
• Given a list of strings, write a function to return the most common character in the list. If there is a tie, return any one of the most common characters. Provide a solution that runs in O(n) time complexity and uses O(1) space complexity.
• Implement a simple text editor that supports the following operations: insert, delete, and move cursor left/right. The editor should maintain the current state of the text after each operation.

Here's how we suggest you approach this round:

• Spend 5-10 minutes discussing and understanding the problem by asking clarifying questions and taking notes.
• Allocate 20 minutes to implement your solution. Use your notes and any provided resources to build your solution. It is important to write clean, concise and efficient code.
• Allocate 10 minutes to unit testing and refactoring your code. This step will help you identify any bugs and optimize your code for better performance.
• Use the final 10 minutes to ask your interviewer any questions you may have about the problem, your solution, or the interview process.

Moving on to the next round—

System Design Interview 

During the system design round of your onsite interview for a Square Software Engineer position, you will be asked questions about building scalable systems and applications. Expect questions on topics such as caching, sharding, network protocols and security, scaling systems, databases, and case studies.

This round is designed to evaluate your knowledge of core distributed systems and your ability to design systems that are scalable, reliable, and secure. You will be expected to demonstrate your understanding of how to design and implement systems that can handle high traffic and user demand while maintaining performance and reliability.

Here's a few examples of system design interview questions to give you an idea:

• How would you design a scalable messaging system for a social media platform that can handle high volumes of data with low latency?
• If you were tasked with building a fault-tolerant e-commerce website, what factors would you consider in the design, and how would you ensure that the site remains available even during high-traffic periods?
• Can you walk me through the process of designing a secure and scalable authentication system for a large enterprise application?
• What are some of the key challenges you would face in designing a recommendation system for a streaming media platform, and how would you overcome these challenges?
• If you were asked to design a fault-tolerant distributed file storage system, how would you approach the problem and what factors would you consider in your design?
• Can you describe how you would design a real-time monitoring and analysis system for network traffic, and what technologies or frameworks you might use to implement such a system?

Behavioral Interview

It is basically a "project experience" interview; it focuses on evaluating your past experiences with challenging projects, workplace-related circumstances, relationships with coworkers and superiors, and other general personality traits to determine if you are a good fit for the position. 

Your goals and long-term vision is also a key element of this round; Square's values candidates who are inspired by the company's purpose of economic empowerment. It seeks software engineers with divergent perspectives, experiences, and backgrounds to help shape the future for its sellers.

Here are a few common questions you can expect here:

• Why do you want to work at Square?
• Why should we hire you? 
• Tell me about a time when you had to deal with a difficult team member. How did you handle the situation, and what was the outcome?
• Describe a situation where you had to work with a tight deadline. How did you manage your time effectively to complete the project on time?
• Tell me about a time when you had to communicate technical information to a non-technical team member or stakeholder. How did you ensure they understood the information?
• Describe a situation where you had to make a difficult decision that had an impact on your team or project. How did you approach the decision-making process, and what was the outcome?

To perform well in this round, it is important to review your past experiences and identify examples that demonstrate your abilities in areas such as leadership, problem-solving, and communication

In addition to this, standard practice in simulated interview conditions where an interviewer asks you a variety of behavioral questions can help you prepare for the Square Software Engineer interview.

You can schedule 1:1 mock interviews with hiring managers and senior software engineers at Square and other FAANG companies to receive valuable feedback on your responses, identify areas for improvement, and gain confidence in your abilities.

Practice with a Square SWE — Get the expert feedback and insights you need to succeed!