Stash Invest Software Engineer Interview Questions + Guide in 2025

Stash Invest is dedicated to empowering individuals to take control of their financial future through accessible investment opportunities and user-friendly technology.

As a Software Engineer at Stash Invest, you will play a pivotal role in developing innovative solutions that enhance the investment experience for users. Your key responsibilities will include designing, coding, testing, and maintaining software applications that align with the company's mission of financial empowerment. You will collaborate closely with cross-functional teams, including product managers and designers, to create intuitive and scalable applications.

To be successful in this role, a strong foundation in algorithms is essential, as you will be required to implement efficient and effective code. Proficiency in Python is also necessary, as it is a core language used in the development process. Familiarity with SQL will be beneficial for managing and querying databases. Additionally, a solid understanding of statistics and probability can enhance your ability to work with data-driven features and contribute to analytical tasks.

Ideal candidates will possess a problem-solving mindset, adaptability to evolving technology, and a passion for creating impactful user experiences. Strong communication skills are vital, as you will need to articulate technical concepts to non-technical stakeholders effectively.

This guide will help you prepare for your interview by focusing on the specific skills and traits that Stash Invest values in its Software Engineers, providing you with insights to stand out as a candidate.

The interview process for a Software Engineer at Stash Invest is structured to assess both technical skills and cultural fit within the company. The process typically includes several key stages:

1. Initial Recruiter Screen

The first step is a phone interview with a recruiter, which usually lasts around 30 minutes. During this conversation, the recruiter will discuss the role in detail, including the expectations and responsibilities associated with the position. They will also evaluate your background, skills, and motivations to ensure alignment with Stash's culture and values. This is an opportunity for you to ask questions about the company and the team dynamics.

2. Technical Assessment

Following the initial screen, candidates typically undergo a technical assessment, which may be conducted through a coding platform like Karat. This assessment focuses on your coding abilities, problem-solving skills, and understanding of algorithms. Expect to tackle coding challenges that may include data structures and algorithms, as well as language-specific questions relevant to the technologies used at Stash.

3. Onsite Interviews

The onsite interview process generally consists of three rounds, each lasting approximately 45 minutes to an hour. The first round often involves pair programming, where you will collaborate with an engineer to solve a coding problem in real-time. This assesses not only your technical skills but also your ability to communicate and work effectively with others.

The second round typically focuses on system design, where you will be asked to design a system or architecture for a given problem. This round evaluates your understanding of software engineering principles, scalability, and best practices in system design.

The final round is usually a behavioral interview, where you will discuss your past experiences, teamwork, and how you handle challenges. This round is crucial for assessing your fit within the Stash culture and your approach to collaboration and problem-solving.

As you prepare for these interviews, be ready to showcase your technical expertise and your ability to work well in a team environment.

Next, let's delve into the specific interview questions that candidates have encountered during the process.

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

Understand the Company Culture

Stash Invest values innovation and collaboration, so it's essential to demonstrate your ability to work well in a team-oriented environment. Familiarize yourself with their mission and values, and be prepared to discuss how your personal values align with theirs. Engaging with the company’s community initiatives or recent projects can also provide you with relevant talking points that show your genuine interest in the company.

Prepare for Technical Assessments

As a Software Engineer, you will likely face a coding screen followed by multiple rounds of technical interviews, including pair programming and system design. Brush up on your algorithms and data structures, as these are critical for success. Practice coding problems on platforms like LeetCode or HackerRank, focusing on easy to medium-level questions, especially those involving hashmaps and other common data structures.

Master the Art of Pair Programming

During the pair programming session, communication is key. Be sure to articulate your thought process clearly as you work through problems. This not only showcases your technical skills but also your ability to collaborate effectively. Practice coding with a partner to simulate this experience and get comfortable explaining your reasoning and decisions.

Anticipate Behavioral Questions

Expect behavioral questions that assess your problem-solving skills and how you handle challenges. Use the STAR (Situation, Task, Action, Result) method to structure your responses. Reflect on past experiences where you successfully navigated obstacles or contributed to team success, particularly in a tech environment. This will help you convey your experience in a compelling way.

Stay Calm Under Pressure

Interviews can be nerve-wracking, especially with the potential for long sessions. If you find yourself freezing during a coding question, take a deep breath and give yourself a moment to collect your thoughts. It’s perfectly acceptable to ask clarifying questions or to talk through your thought process, even if you’re unsure. This shows your analytical skills and willingness to engage with the problem.

Follow Up Thoughtfully

After your interview, send a thank-you note to your interviewers, expressing appreciation for their time and reiterating your interest in the role. This not only demonstrates professionalism but also keeps you on their radar. If you have specific insights or ideas that came to mind during the interview, feel free to include those as well.

By preparing thoroughly and approaching the interview with confidence and clarity, you can position yourself as a strong candidate for the Software Engineer role at Stash Invest. Good luck!

In this section, we’ll review the various interview questions that might be asked during a Software Engineer interview at Stash Invest. The interview process will likely focus on your technical skills, problem-solving abilities, and how you work within a team. Be prepared to demonstrate your knowledge of algorithms, coding proficiency, and system design, as well as your ability to communicate effectively.

Algorithms and Data Structures

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

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

How to Answer

Discuss the characteristics of both data structures, including their use cases and how they operate (LIFO vs. FIFO).

Example

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

2. Describe a time you optimized an algorithm. What was the original algorithm, and how did you improve it?

This question assesses your problem-solving skills and understanding of algorithm efficiency.

How to Answer

Provide a specific example, detailing the original algorithm's complexity and the changes you made to enhance its performance.

Example

“I was working on a sorting algorithm that had a time complexity of O(n^2). I researched and implemented a quicksort algorithm, which reduced the time complexity to O(n log n). This significantly improved the performance of our application, especially with larger datasets.”

3. How would you approach solving a problem where you need to find the longest substring without repeating characters?

This question tests your coding skills and ability to think algorithmically.

How to Answer

Outline your thought process, including any algorithms or data structures you would use to solve the problem.

Example

“I would use a sliding window approach with a hash map to track the characters and their indices. As I iterate through the string, I would expand the window until I encounter a repeating character, at which point I would adjust the start of the window to ensure all characters remain unique.”

4. What is the time complexity of accessing an element in an array versus a linked list?

This question evaluates your understanding of data structure performance.

How to Answer

Discuss the differences in time complexity for both data structures and the implications for their use.

Example

“Accessing an element in an array is O(1) because arrays allow direct indexing. In contrast, accessing an element in a linked list is O(n) since you must traverse the list from the head to reach the desired node.”

5. Can you explain what a binary search tree is and how it differs from a regular binary tree?

This question assesses your knowledge of tree data structures.

How to Answer

Define a binary search tree and highlight its properties compared to a regular binary tree.

Example

“A binary search tree (BST) is a binary tree where each node has a maximum of two children, and the left child is less than the parent node while the right child is greater. This property allows for efficient searching, insertion, and deletion operations, typically O(log n) in balanced trees, unlike a regular binary tree where no such ordering is guaranteed.”

System Design

1. How would you design a URL shortening service?

This question tests your system design skills and ability to think through complex problems.

How to Answer

Outline the components of the system, including database design, API endpoints, and scalability considerations.

Example

“I would start by defining the core functionality: taking a long URL and returning a shorter version. I would use a hash function to generate a unique key for each URL and store it in a database. The API would have endpoints for creating and retrieving URLs. For scalability, I would consider using a distributed database and caching frequently accessed URLs.”

2. Describe how you would design a chat application. What are the key components?

This question evaluates your understanding of real-time communication systems.

How to Answer

Discuss the architecture, including client-server communication, data storage, and user authentication.

Example

“I would design the chat application using a client-server architecture. The server would handle user authentication and message storage, while WebSocket connections would enable real-time communication. I would also implement a database to store user data and chat history, ensuring data consistency and reliability.”

3. What considerations would you take into account when designing a scalable web application?

This question assesses your knowledge of scalability and performance optimization.

How to Answer

Discuss various factors such as load balancing, database optimization, and caching strategies.

Example

“When designing a scalable web application, I would consider load balancing to distribute traffic evenly across servers, using a CDN for static content delivery, and optimizing database queries. Additionally, I would implement caching strategies to reduce database load and improve response times.”

4. How would you handle data consistency in a distributed system?

This question tests your understanding of distributed systems and data integrity.

How to Answer

Discuss concepts like eventual consistency, CAP theorem, and strategies for maintaining data integrity.

Example

“In a distributed system, I would implement eventual consistency to ensure that all nodes eventually reflect the same data. I would also use techniques like distributed transactions or consensus algorithms to maintain data integrity, while being mindful of the trade-offs outlined in the CAP theorem.”

5. Can you explain the microservices architecture and its advantages?

This question evaluates your knowledge of modern software architecture.

How to Answer

Define microservices and discuss their benefits compared to monolithic architectures.

Example

“Microservices architecture involves breaking down an application into smaller, independent services that communicate over APIs. This approach allows for greater flexibility, easier scaling, and the ability to deploy services independently, which can lead to faster development cycles and improved fault isolation.”