Simpl Software Engineer Interview Guide

The 60-second brief

A Software Engineer at Simpl plays a pivotal role in shaping the company's financial technology products and services. You will be responsible for designing, developing, and maintaining software solutions that enhance user experiences and drive business growth. This position is critical as it directly impacts how Simpl interacts with its customers, streamlining payment processes and ensuring secure transactions. Your contributions will support various applications, including the Pay Later service, which allows customers to make purchases with deferred payments. As a Software Engineer, you will face complex challenges that require innovative solutions. Whether it’s improving system performance, architecting scalable solutions, or integrating new technologies, your work will significantly influence Simpl's ability to offer exceptional financial services.

This guide is scoped to a Software Engineer candidate at Simpl.

Focus areas

• Data Structures & Algorithms (DSA)
• System Design
• Java

The Simpl interview process

Simpl candidates report 4 rounds over 3-5 weeks. The stages below are what candidates describe, not a published process.

Technical Assessments

Candidates undergo technical assessments to evaluate their coding skills.

What to demonstrate

• Candidates undergo technical assessments to evaluate their coding skills
• Depth in Data Structures & Algorithms (DSA)

How to prepare

• Answer aloud and timed: What is the difference between a stack and a queue?
• Answer aloud and timed: Explain the concept of database normalization and its importance.

Coding Challenges

Participants complete coding challenges to demonstrate their problem-solving abilities.

What to demonstrate

• Participants complete coding challenges to demonstrate their problem-solving abilities
• Depth in Data Structures & Algorithms (DSA)

How to prepare

• Answer aloud and timed: Can you describe how you would optimize a SQL query?
• Answer aloud and timed: What are the principles of RESTful API design?

Team Discussions

Candidates engage in discussions with team members to assess cultural fit.

What to demonstrate

• Candidates engage in discussions with team members to assess cultural fit
• Depth in Data Structures & Algorithms (DSA)

How to prepare

• Answer aloud and timed: Discuss your experience with microservices architecture.
• Answer aloud and timed: Design a payment processing system for an e-commerce platform.

Behavioral Interviews

Interviews explore past experiences and teamwork dynamics.

What to demonstrate

• Interviews explore past experiences and teamwork dynamics
• Depth in Data Structures & Algorithms (DSA)

How to prepare

• Prepare three examples from your own work, each with a decision you made and an outcome you can quantify.
• Re-read the description of the behavioral interviews above and write down what you would ask to confirm before it.

Where candidates lose points

Practice coding under time constraints

Develop your ability to solve problems quickly and efficiently, as many interviews will involve timed coding challenges.

Prepare for behavioral questions

Reflect on your past experiences and be ready to discuss how they shape your approach to work and collaboration.

Show enthusiasm for Simpl's mission

Understand the company’s products and values, and express your passion for contributing to its goals.

Questions & practice

Given an array of integers, how would you find the maximum product of any two numbers?

Medium · Problem-Solving / Case Studies

Approach

1. Restate the input: its shape, its size, and what is guaranteed about it.
2. Name the brute-force solution and its complexity before improving on it.
3. Choose the data structure from the access pattern, not from familiarity.
4. State the target complexity and say which constraint rules the naive version out.

Follow-up

• How does this change if the input no longer fits in memory?
• What is the worst case, and how likely is it on real data?

Solve a problem involving depth-first search on a graph.

Medium · Coding / Algorithms

Approach

1. Restate the input: its shape, its size, and what is guaranteed about it.
2. Name the brute-force solution and its complexity before improving on it.
3. Choose the data structure from the access pattern, not from familiarity.
4. State the target complexity and say which constraint rules the naive version out.

Follow-up

• How does this change if the input no longer fits in memory?
• What is the worst case, and how likely is it on real data?

Write a function to check if a string is a palindrome.

Medium · Coding / Algorithms

Approach

1. Restate the input: its shape, its size, and what is guaranteed about it.
2. Name the brute-force solution and its complexity before improving on it.
3. Choose the data structure from the access pattern, not from familiarity.
4. State the target complexity and say which constraint rules the naive version out.

Follow-up

• How does this change if the input no longer fits in memory?
• What is the worst case, and how likely is it on real data?

Implement a binary search algorithm.

Medium · Coding / Algorithms

Approach

1. Restate the input: its shape, its size, and what is guaranteed about it.
2. Name the brute-force solution and its complexity before improving on it.
3. Choose the data structure from the access pattern, not from familiarity.
4. State the target complexity and say which constraint rules the naive version out.

Follow-up

• How does this change if the input no longer fits in memory?
• What is the worst case, and how likely is it on real data?

Explain the concept of database normalization and its importance.

Medium · Technical / Domain Questions

Approach

1. Name the grain you start from and join outward from it.
2. Check whether any join is one-to-many before aggregating, or the sums inflate.
3. Say which index the query would use, and what makes it unusable.
4. Handle the rows that do not match: that is usually the actual question.

Follow-up

• How does the query change if that join becomes one-to-many?
• What happens to this when the table is ten times larger?

Can you describe how you would optimize a SQL query?

Medium · Technical / Domain Questions

Approach

1. Name the grain you start from and join outward from it.
2. Check whether any join is one-to-many before aggregating, or the sums inflate.
3. Say which index the query would use, and what makes it unusable.
4. Handle the rows that do not match: that is usually the actual question.

Follow-up

• How does the query change if that join becomes one-to-many?
• What happens to this when the table is ten times larger?

What is the difference between a stack and a queue?

Medium · Technical / Domain Questions

Approach

1. Clarify what is being asked and what a complete answer contains.
2. State your assumptions explicitly before working the problem.
3. Say what you would check first and why it is the highest-information step.
4. Work from the requirement backwards to the design.

Follow-up

• What assumption would you test first?
• How would you know your answer was wrong?

What are the principles of RESTful API design?

Medium · Technical / Domain Questions

Approach

1. Say who the caller is and what they do when the call fails halfway.
2. Define the identity of a request so a retry cannot double-apply it.
3. Separate accepted, pending, failed and confirmed; they are different facts.
4. Design the error taxonomy before the success shape; callers branch on it.

Follow-up

• What happens if the caller retries after a timeout?
• How does a client discover it is on an old version of this contract?

Discuss your experience with microservices architecture.

Medium · Technical / Domain Questions

Approach

1. Fix the scope first: who calls this, how often, and what they do when it fails.
2. Name the read and write paths separately; they rarely have the same bottleneck.
3. Choose a partition key and say what query it makes expensive.
4. State the consistency you need, and where you are willing to be stale.

Follow-up

• What breaks first when traffic grows ten times?
• How does this behave when that dependency is down for an hour?

Design a payment processing system for an e-commerce platform.

Medium · System Design / Architecture

Approach

1. Fix the scope first: who calls this, how often, and what they do when it fails.
2. Name the read and write paths separately; they rarely have the same bottleneck.
3. Choose a partition key and say what query it makes expensive.
4. State the consistency you need, and where you are willing to be stale.

Follow-up

• What breaks first when traffic grows ten times?
• How does this behave when that dependency is down for an hour?

How would you architect a service like Uber or a ride-sharing application?

Medium · System Design / Architecture

Approach

1. Fix the scope first: who calls this, how often, and what they do when it fails.
2. Name the read and write paths separately; they rarely have the same bottleneck.
3. Choose a partition key and say what query it makes expensive.
4. State the consistency you need, and where you are willing to be stale.

Follow-up

• What breaks first when traffic grows ten times?
• How does this behave when that dependency is down for an hour?

Describe how you would handle high availability and disaster recovery in your system.

Medium · System Design / Architecture

Approach

1. Fix the scope first: who calls this, how often, and what they do when it fails.
2. Name the read and write paths separately; they rarely have the same bottleneck.
3. Choose a partition key and say what query it makes expensive.
4. State the consistency you need, and where you are willing to be stale.

Follow-up

• What breaks first when traffic grows ten times?
• How does this behave when that dependency is down for an hour?

What considerations would you have for data consistency in a distributed system?

Medium · System Design / Architecture

Approach

1. Fix the scope first: who calls this, how often, and what they do when it fails.
2. Name the read and write paths separately; they rarely have the same bottleneck.
3. Choose a partition key and say what query it makes expensive.
4. State the consistency you need, and where you are willing to be stale.

Follow-up

• What breaks first when traffic grows ten times?
• How does this behave when that dependency is down for an hour?

How would you approach debugging a complex system issue?

Medium · Problem-Solving / Case Studies

Approach

1. Establish what changed and when, before forming any theory.
2. Pick a bisection that eliminates candidates whichever way it turns out.
3. Check the instrumentation before believing the symptom.
4. Separate the trigger from the cause; the deploy is rarely the bug.

Follow-up

• What would you look at first, and what would it rule out?
• How would you tell a cause from a coincidence here?

Suggested practice checklist

Built from the rounds and topics Simpl candidates report.

Day 1 — Map the Simpl loop

• Write out the reported sequence: Technical Assessments, Coding Challenges, Team Discussions, Behavioral Interviews.
• For each round, write one sentence on what it is judging, from the description above, and mark the one you are least ready for.

Deliverable: A one-page map of the 4 reported rounds, with the weakest marked.

Day 2 — Work Data Structures & Algorithms (DSA)

• Spend the session on Data Structures & Algorithms (DSA), which Simpl candidates report being tested on.
• Write one worked example in Data Structures & Algorithms (DSA) and time yourself on it.

Deliverable: One timed worked example in Data Structures & Algorithms (DSA).

Day 3 — Work System Design

• Spend the session on System Design, which Simpl candidates report being tested on.
• Write one worked example in System Design and time yourself on it.

Deliverable: One timed worked example in System Design.

Day 4 — Work Java

• Spend the session on Java, which Simpl candidates report being tested on.
• Write one worked example in Java and time yourself on it.

Deliverable: One timed worked example in Java.

Day 5 — Answer out loud: Technical / Domain Questions

• Answer aloud, timed: What is the difference between a stack and a queue?
• Answer aloud, timed: Explain the concept of database normalization and its importance.

Deliverable: Spoken answers to 2 reported Technical / Domain Questions question(s), under time.

Day 6 — Answer out loud: System Design / Architecture

• Answer aloud, timed: Design a payment processing system for an e-commerce platform.
• Answer aloud, timed: How would you architect a service like Uber or a ride-sharing application?

Deliverable: Spoken answers to 2 reported System Design / Architecture question(s), under time.

Day 7 — Answer out loud: Behavioral / Leadership

• Answer aloud, timed: Describe a time you faced a significant challenge in a project. How did you overcome it?
• Answer aloud, timed: How do you prioritize tasks when working on multiple projects?

Deliverable: Spoken answers to 2 reported Behavioral / Leadership question(s), under time.

Behavioural preparation

Behavioural rounds judge the decision you made and what it cost.

Describe a time you faced a significant challenge in a project. How did you overcome it?

Medium · Behavioral / Leadership

Approach

1. Pick a story where you made the decision, not one where you watched it.
2. State the situation in two sentences and spend the rest on the reasoning.
3. Give the blast radius: what could have broken, and what you measured.
4. Name the disagreement and how you resolved it with evidence.

Follow-up

• What would you do differently if you ran that again?
• How did you know your change caused the improvement?

How do you prioritize tasks when working on multiple projects?

Medium · Behavioral / Leadership

Approach

1. Pick a story where you made the decision, not one where you watched it.
2. State the situation in two sentences and spend the rest on the reasoning.
3. Give the blast radius: what could have broken, and what you measured.
4. Name the disagreement and how you resolved it with evidence.

Follow-up

• What would you do differently if you ran that again?
• How did you know your change caused the improvement?

Tell me about a time you had to collaborate with a difficult team member.

Medium · Behavioral / Leadership

Approach

1. Pick a story where you made the decision, not one where you watched it.
2. State the situation in two sentences and spend the rest on the reasoning.
3. Give the blast radius: what could have broken, and what you measured.
4. Name the disagreement and how you resolved it with evidence.

Follow-up

• What would you do differently if you ran that again?
• How did you know your change caused the improvement?

Discuss a time when you had to learn a new technology quickly to complete a project.

Medium · Problem-Solving / Case Studies

Approach

1. Pick a story where you made the decision, not one where you watched it.
2. State the situation in two sentences and spend the rest on the reasoning.
3. Give the blast radius: what could have broken, and what you measured.
4. Name the disagreement and how you resolved it with evidence.

Follow-up

• What would you do differently if you ran that again?
• How did you know your change caused the improvement?