FreeWheel Software Engineer Interview Guide

The 60-second brief

A Software Engineer at FreeWheel plays a crucial role in developing and maintaining the company’s technology solutions that drive the advertising ecosystem. This position is essential for enhancing the effectiveness of digital advertising by creating robust software that supports various platforms and users. You will work on complex problems, such as optimizing ad delivery, ensuring seamless integration with third-party services, and improving user experiences. As a Software Engineer, your work directly impacts the efficiency and reliability of FreeWheel’s products, which are relied upon by numerous clients across the advertising landscape. You will contribute to high-scale distributed systems, collaborating with cross-functional teams to deliver solutions that are innovative and user-focused.

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

Focus areas

• Data Structures (DS)
• Algorithms
• Python

The FreeWheel interview process

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

Initial Screening

Conducted by HR or a recruiter to evaluate basic qualifications.

What to demonstrate

• Conducted by HR or a recruiter to evaluate basic qualifications
• Depth in Data Structures (DS)

How to prepare

• Be able to walk your CV end to end in two minutes, and say why this company specifically.
• Have your salary expectations, notice period and location constraints ready, and ask for the rest of the loop in writing.

Technical Assessments

Includes coding challenges or online assessments to test technical skills.

What to demonstrate

• Includes coding challenges or online assessments to test technical skills
• Depth in Data Structures (DS)

How to prepare

• Answer aloud and timed: Describe how you would optimize a SQL query for performance.
• Answer aloud and timed: Write a function to reverse a linked list.

Technical Interviews

Real-time problem solving and discussions on technical knowledge.

What to demonstrate

• Real-time problem solving and discussions on technical knowledge
• Depth in Data Structures (DS)

How to prepare

• Answer aloud and timed: Given an array of integers, find two numbers such that they add up to a specific target.
• Answer aloud and timed: Implement a binary search algorithm.

Team and Leadership Meetings

Meet with team members and leadership to assess cultural fit and discuss experiences.

What to demonstrate

• Meet with team members and leadership to assess cultural fit and discuss experiences
• Depth in Data Structures (DS)

How to prepare

• Answer aloud and timed: Design a scalable notification system.
• Answer aloud and timed: How would you structure a microservices architecture for an ad-serving platform?

Where candidates lose points

Be Prepared for Technical Depth

Expect to dive deep into technical questions. Brush up on algorithms, data structures, and system design concepts to ensure you can articulate your thought process clearly.

Showcase Your Projects

Be ready to discuss your previous work and how it relates to the role. Highlight specific challenges you faced and the impact of your contributions.

Practice Behavioral Questions

Prepare for behavioral interview questions by using the STAR method (Situation, Task, Action, Result) to structure your responses effectively.

Engage with Interviewers

Show interest in the role and company by asking thoughtful questions. This not only demonstrates your enthusiasm but also helps you gauge if FreeWheel is the right fit for you.

Questions & practice

Explain the difference between a process and a thread.

Medium · Technical / Domain Questions

Approach

1. Say what the runtime actually does before reasoning about the code.
2. Name what is shared across threads and what owns each piece of state.
3. Identify the window where an invariant is briefly untrue.
4. Distinguish a value from a reference to it, and say which one you handed out.

Follow-up

• What happens if two callers reach this at the same time?
• Where could this allocate more than you expect?

Write a function to reverse a linked list.

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?

Given an array of integers, find two numbers such that they add up to a specific target.

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?

Describe how you would optimize a SQL query for performance.

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?

Discuss the trade-offs of using SQL vs. NoSQL databases in your design.

Medium · System Design / Architecture

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 significance of RESTful APIs in web applications?

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?

Design a scalable notification 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 structure a microservices architecture for an ad-serving 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?

If given a tight deadline, how would you ensure quality in your deliverables?

Medium · Problem-Solving / Case Studies

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?

How would you approach debugging a critical issue in production?

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 FreeWheel candidates report.

Day 1 — Map the FreeWheel loop

• Write out the reported sequence: Initial Screening, Technical Assessments, Technical Interviews, Team and Leadership Meetings.
• 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 (DS)

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

Deliverable: One timed worked example in Data Structures (DS).

Day 3 — Work Algorithms

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

Deliverable: One timed worked example in Algorithms.

Day 4 — Work Python

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

Deliverable: One timed worked example in Python.

Day 5 — Answer out loud: Technical / Domain Questions

• Answer aloud, timed: Explain the difference between a process and a thread.
• Answer aloud, timed: What is the significance of RESTful APIs in web applications?

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

Day 6 — Answer out loud: Coding / Algorithms

• Answer aloud, timed: Write a function to reverse a linked list.
• Answer aloud, timed: Given an array of integers, find two numbers such that they add up to a specific target.

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

Day 7 — Answer out loud: System Design / Architecture

• Answer aloud, timed: Design a scalable notification system.
• Answer aloud, timed: How would you structure a microservices architecture for an ad-serving platform?

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

Behavioural preparation

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

Describe a challenging project you worked on and how you overcame obstacles.

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 managing 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?

Give an example of how you handled a conflict within a team.

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?