Interview guides · Marvin

Marvin Software Engineer Interview Guide

Marvin Software Engineer interview guide: reported rounds, questions and how candidates describe the process.

The 60-second brief

As a Software Engineer at Marvin, you are at the intersection of precision engineering and high-quality manufacturing. You contribute to the digital infrastructure that powers the creation of industry-leading window and door products. Your work directly impacts how internal teams operate, how we maintain our manufacturing efficiency, and how we leverage technology to solve complex physical-world problems. This role is critical to the Marvin mission of providing exceptional experiences through superior craftsmanship. You will work within a collaborative environment where technical problem-solving is balanced with a deep respect for operational excellence. Whether you are optimizing internal software systems or developing tools for our engineering teams, you will play a central role in driving the innovation that keeps our production lines and business processes running smoothly.

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

Focus areas

Technical Interviewing
Problem Solving (Coding Challenges)
Coding in an Interview Format

The Marvin interview process

Marvin candidates report 6 rounds over 4-6 weeks. The stages below are what candidates describe, not a published process.

Initial Screening

Gauge your background and interest in the position.

What to demonstrate

Gauge your background and interest in the position
Depth in Technical Interviewing

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

Participate in a series of technical evaluations to demonstrate your skills.

What to demonstrate

Participate in a series of technical evaluations to demonstrate your skills
Depth in Technical Interviewing

How to prepare

Answer aloud and timed: What is your experience with software architecture in a manufacturing or industrial environment?
Answer aloud and timed: Describe a time you had to optimize a piece of code for better performance.

Behavioral Assessments

Engage in discussions to assess your values and past experiences.

What to demonstrate

Engage in discussions to assess your values and past experiences
Depth in Technical Interviewing

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 assessments above and write down what you would ask to confirm before it.

Video Calls

Conduct interviews via video calls to evaluate your fit for the role.

What to demonstrate

Conduct interviews via video calls to evaluate your fit for the role
Depth in Technical Interviewing

How to prepare

Answer aloud and timed: How do you handle situations where you disagree with a team member’s technical approach?
Answer aloud and timed: Describe a situation where you had to manage a tight deadline while maintaining code quality.

In-Person Visit

Depending on the role and location, you may visit one of our facilities.

What to demonstrate

Depending on the role and location, you may visit one of our facilities
Depth in Technical Interviewing

How to prepare

Answer aloud and timed: Why are you interested in working for Marvin specifically?
Answer aloud and timed: Tell me about a time you took the initiative to improve a process or workflow.

Final Decision

Receive communication regarding the outcome of your interview process.

What to demonstrate

Receive communication regarding the outcome of your interview process
Depth in Technical Interviewing

How to prepare

Answer aloud and timed: Describe your process for approaching a new coding challenge or LC-style problem.
Answer aloud and timed: How do you handle ambiguity when requirements are not fully defined?

Where candidates lose points

Be Prompt

Whether it is a phone call or a video interview, treat your start time as a hard deadline. Punctuality is a sign of respect and professionalism at Marvin.

Review Fundamentals

Do not over-index on obscure trivia. Focus on core concepts like OOP, memory management, and clean coding standards.

Ask Questions

Prepare 3–5 thoughtful questions about the team, the company’s technical challenges, or the manufacturing process. This demonstrates genuine engagement.

Be Honest

If you do not know the answer to a technical question, explain how you would go about finding the answer. We value curiosity and resourcefulness.

Questions & practice

Describe your process for approaching a new coding challenge or LC-style problem.

Medium · Problem-Solving and Coding

Approach

Restate the input: its shape, its size, and what is guaranteed about it.
Name the brute-force solution and its complexity before improving on it.
Choose the data structure from the access pattern, not from familiarity.
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?

Walk me through a challenging technical project you led from start to finish.

Medium · Problem-Solving and Coding

Approach

Restate the input: its shape, its size, and what is guaranteed about it.
Name the brute-force solution and its complexity before improving on it.
Choose the data structure from the access pattern, not from familiarity.
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?

If you were tasked with automating a manual task on the factory floor, where would you start?

Medium · Problem-Solving and Coding

Approach

Restate the input: its shape, its size, and what is guaranteed about it.
Name the brute-force solution and its complexity before improving on it.
Choose the data structure from the access pattern, not from familiarity.
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?

Find version gaps and relay lag with window functions

Medium · window functions · event tables · frame semantics

outbox_event holds event_id, aggregate_type, aggregate_id, aggregate_version, event_type, payload, status ('pending','published','dead'), attempts, created_at, published_at. A projection is missing rows and you must decide whether the relay skipped events or the consumer dropped them. Write three queries over the last seven days: one listing every aggregate_id whose published aggregate_version sequence has a hole, one giving per-day counts with a running total, and one returning the newest published event per aggregate. For each, say where the window function is evaluated relative to WHERE and LIMIT. PostgreSQL 16.

Approach

Gaps: compute lead(aggregate_version) OVER (PARTITION BY aggregate_id ORDER BY aggregate_version) in a subquery, then filter next_version <> aggregate_version + 1 in the outer query. Window functions are evaluated after WHERE, GROUP BY and HAVING and before the outer ORDER BY and LIMIT, so the predicate cannot sit in the same WHERE clause and PostgreSQL 16 has no QUALIFY.
Say what the seven-day filter does to the answer: it truncates every partition, so the first row per aggregate has no predecessor inside the window and a hole spanning the boundary is invisible. Widen the window, or join to resource.version as the authority for the true maximum.
Running total: SELECT date_trunc('day', created_at) AS d, count() AS n, sum(count()) OVER (ORDER BY date_trunc('day', created_at) ROWS UNBOUNDED PRECEDING). An aggregate inside a window call is legal because grouping runs before windowing. The grouping key is unique per row here so ROWS and RANGE agree, but write the frame anyway — over ungrouped rows with tied timestamps the default RANGE frame pulls in every peer row and the total jumps.
Newest per aggregate: DISTINCT ON (aggregate_id) ... ORDER BY aggregate_id, aggregate_version DESC is the cheap PostgreSQL-only form when an index matches that order; row_number() OVER (PARTITION BY aggregate_id ORDER BY aggregate_version DESC) = 1 is the portable form and needs a subquery for the same evaluation-order reason as the gap query.

Follow-up

Relay failover redelivers events. Does a duplicate break the gap query, and how would you detect one from this table alone?
Turn the gap check into a continuous monitor rather than a query someone runs after an incident. What does it watch?

Stop tag and share joins from fanning out a page

Medium · join fan-out · semi-joins · many-to-many

resource_tag is (resource_id, tag_id) with PK (resource_id, tag_id); resource_share is (resource_id, shared_with_user_id, permission). The tagged-and-shared listing inner-joins resource to both, filters tenant_id, tag_id = ANY($2) and shared_with_user_id = $3, orders by updated_at DESC and takes 50. Pages come back with fewer than 50 distinct resources and the total in the header is far too high. Explain the row multiplication, rewrite both the page query and the count query so each is correct, and name the index each one needs. PostgreSQL 16.

Approach

Do the arithmetic against the predicates that are actually there. An inner join emits one row per matching child row, and both joins are filtered: tag_id = ANY($2) admits only the requested tags, shared_with_user_id = $3 admits one user's share rows. So a resource holding three of the requested tags and shared with $3 once yields three rows, not one — the multiplier is its count of matching tags times its share rows for that single user, and that second factor is 1 unless the table admits duplicate (resource_id, shared_with_user_id) pairs. LIMIT 50 then limits rows rather than resources, and COUNT(*) counts pairs — the header is the product, not the population.
Reject DISTINCT as the fix. It deduplicates after the product has been built, so the planner must materialise and sort the fanned-out set before the LIMIT can apply, and it leaves any SUM or AVG in the same select list wrong.
Rewrite both filters as semi-joins, keeping resource as the only row source: AND EXISTS (SELECT 1 FROM resource_tag rt WHERE rt.resource_id = r.resource_id AND rt.tag_id = ANY($2)) and the same shape against resource_share. A semi-join stops at the first match per resource and preserves the driving index order, so ORDER BY updated_at DESC, resource_id DESC LIMIT 50 still stops after 50 rows.
Count with the same predicates and no join at all: SELECT count(*) FROM resource r WHERE r.tenant_id = $1 AND r.status = 'active' AND EXISTS (...) AND EXISTS (...). Nothing multiplies a resource, so the number is the population.

Follow-up

The filter changes from 'any of these tags' to 'all of these tags'. Rewrite it and state what it costs relative to the ANY form.
A resource can be shared with the same user twice under different permissions. Does your count change, and should it?

Can you explain the concepts of inheritance and polymorphism in C++?

Medium · Technical and Domain Knowledge

Approach

Clarify what is being asked and what a complete answer contains.
State your assumptions explicitly before working the problem.
Say what you would check first and why it is the highest-information step.
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 do you ensure your code is maintainable and scalable for future developers?

Medium · Technical and Domain Knowledge

Approach

Fix the scope first: who calls this, how often, and what they do when it fails.
Name the read and write paths separately; they rarely have the same bottleneck.
Choose a partition key and say what query it makes expensive.
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 legacy codebase that lacks documentation?

Medium · Technical and Domain Knowledge

Approach

Establish what changed and when, before forming any theory.
Pick a bisection that eliminates candidates whichever way it turns out.
Check the instrumentation before believing the symptom.
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 Marvin candidates report.

Day 1 — Map the Marvin loop

Write out the reported sequence: Initial Screening, Technical Assessments, Behavioral Assessments, Video Calls, In-Person Visit, Final Decision.
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 6 reported rounds, with the weakest marked.

Day 2 — Work Technical Interviewing

Spend the session on Technical Interviewing, which Marvin candidates report being tested on.
Write one worked example in Technical Interviewing and time yourself on it.

Deliverable: One timed worked example in Technical Interviewing.

Day 3 — Work Problem Solving (Coding Challenges)

Spend the session on Problem Solving (Coding Challenges), which Marvin candidates report being tested on.
Write one worked example in Problem Solving (Coding Challenges) and time yourself on it.

Deliverable: One timed worked example in Problem Solving (Coding Challenges).

Day 4 — Work Coding in an Interview Format

Spend the session on Coding in an Interview Format, which Marvin candidates report being tested on.
Write one worked example in Coding in an Interview Format and time yourself on it.

Deliverable: One timed worked example in Coding in an Interview Format.

Day 5 — Answer out loud: Technical and Domain Knowledge

Answer aloud, timed: Can you explain the concepts of inheritance and polymorphism in C++?
Answer aloud, timed: How would you approach debugging a legacy codebase that lacks documentation?

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

Day 6 — Answer out loud: Behavioral and Cultural Fit

Answer aloud, timed: Tell me about a time you had to explain a complex technical problem to a non-technical stakeholder.
Answer aloud, timed: How do you handle situations where you disagree with a team member’s technical approach?

Deliverable: Spoken answers to 2 reported Behavioral and Cultural Fit question(s), under time.

Day 7 — Answer out loud: Problem-Solving and Coding

Answer aloud, timed: Describe your process for approaching a new coding challenge or LC-style problem.
Answer aloud, timed: How do you handle ambiguity when requirements are not fully defined?

Deliverable: Spoken answers to 2 reported Problem-Solving and Coding question(s), under time.

Behavioural preparation

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

What is your experience with software architecture in a manufacturing or industrial environment?

Medium · Technical and Domain Knowledge

Approach

Pick a story where you made the decision, not one where you watched it.
State the situation in two sentences and spend the rest on the reasoning.
Give the blast radius: what could have broken, and what you measured.
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?

Describe a time you had to optimize a piece of code for better performance.

Medium · Technical and Domain Knowledge

Approach

Pick a story where you made the decision, not one where you watched it.
State the situation in two sentences and spend the rest on the reasoning.
Give the blast radius: what could have broken, and what you measured.
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?