At Lexington Medical, a Software Engineer plays a pivotal role in bridging the gap between cutting-edge software design and advanced medical hardware. Because the company specializes in producing highly sophisticated, minimally invasive surgical devices—such as the AEON Endostapler—software is not developed in a vacuum. Instead, it directly powers the manufacturing systems, automated testing rigs, and embedded technologies that ensure patient safety and product reliability. You will work in a fast-paced, highly collaborative environment alongside Mechanical Engineers, Quality Managers, and executive leadership to bring life-saving technologies to market. This role requires an understanding of how software interacts with physical components, demanding a high level of precision, rigorous testing, and compliance with strict quality standards. For engineers who thrive on seeing their code impact physical, tangible products that improve human lives, this position offers an incredibly rewarding career path. You will have a direct hand in shaping the internal tools, test systems, and product systems that define the next generation of medical technology.
Introductory Call
reportedInitial conversation with the CEO or a recruiter to discuss your background, career goals, and interest in the medical device industry.
What to demonstrate
- Initial conversation with the CEO or a recruiter to discuss your background, career goals, and interest in the medical device industry
- Depth in Software Engineering (General)
How to prepare
- Answer aloud and timed: Walk me through a complex software project on your resume where you had to interface with physical hardware or strict testing constraints.
- Answer aloud and timed: Describe your experience working in a regulated environment or adhering to strict quality management standards.
Onsite Visit
reportedComprehensive onsite visit starting with a tour of the manufacturing and engineering facility.
What to demonstrate
- Comprehensive onsite visit starting with a tour of the manufacturing and engineering facility
- Depth in Software Engineering (General)
How to prepare
- Answer aloud and timed: What is your approach to documenting your code and ensuring it can be easily audited or validated by quality assurance teams?
- Answer aloud and timed: Tell me about a time you had to debug a system failure where the root cause was unclear. How did you isolate the issue?
Technical Discussion
reportedInterview with a product engineer focusing on technical skills and coding ability.
What to demonstrate
- Interview with a product engineer focusing on technical skills and coding ability
- Depth in Software Engineering (General)
How to prepare
- Answer aloud and timed: How would you design a software-controlled testing rig to validate the mechanical reliability of a surgical stapler?
- Answer aloud and timed: What programming languages and frameworks are you most comfortable using when building internal automation tools?
Quality Session
reportedQuality-focused interview with the Quality Manager to assess fit within the product lifecycle.
What to demonstrate
- Quality-focused interview with the Quality Manager to assess fit within the product lifecycle
- Depth in Software Engineering (General)
How to prepare
- Answer aloud and timed: Explain how you would approach writing a test suite for a system that has both software and hardware dependencies.
- Answer aloud and timed: How do you balance the need for rapid software development with the slow, deliberate pace of hardware validation?
Strategic Vision Conversation
reportedDiscussion with the COO about strategic product vision and alignment with company goals.
What to demonstrate
- Discussion with the COO about strategic product vision and alignment with company goals
- Depth in Software Engineering (General)
How to prepare
- Answer aloud and timed: Why are you interested in working in the medical device space, and what do you think makes software engineering unique in this industry?
- Answer aloud and timed: How do you handle disagreements with hardware engineers or quality managers when defining product requirements?
PracHub editorial advice for the preparation topics above.
Know your resume inside out
Be ready to explain the technical decisions, architecture, and testing methodologies of every project you have listed. Interviewers will ask detailed questions about your past experiences.
Do not exaggerate your experience with hardware or quality systems if you do not have it
Instead, emphasize your willingness to learn and your structured approach to problem-solving.
Show curiosity during the tour
Treat the facility tour as an active part of your interview. Ask insightful questions about the manufacturing equipment, the testing setups, and the challenges the engineering team faces.
Choose a category, try a prompt, then open its approach, worked solution or follow-up when you need it.
Identify the heaviest tenants in a five-minute window under memory pressure
The edge service handles about 3,000 requests per second across roughly 50,000 tenants, peaking near 9,000. Expose the 50 heaviest tenants by request count over the trailing five minutes so limits can be tightened before one tenant's backfill starves the fleet. You may not retain five minutes of raw records. Give the exact solution and its memory, then the bounded-memory approximation with its error stated as a formula, and say which you would ship and at what tenant cardinality that choice changes.
Approach
- Do the exact version first, because it is affordable at this cardinality: a ring of 300 one-second counters per tenant, advanced lazily, is 1,200 bytes of counters per tenant and roughly 60 to 90 MB for 50,000 tenants with overhead. Carry a running total and subtract the bucket you overwrite so a window read is O(1) rather than 300 adds.
- Extract the top 50 with a size-k min-heap over the tenant sums: O(d log k) for d tenants, against O(d log d) to sort them all. Maintaining the heap continuously instead of on query requires a tenant-to-heap-index map, because incrementing a count already inside the heap means sifting from a known position, and without that map you rebuild the heap on every request.
- State the approximation precisely rather than gesturing at sketches. Misra-Gries with m counters retains every item whose true count exceeds N/(m+1), and each retained count underestimates the truth by at most N/(m+1). With m = 1,000 and N = 900,000 requests in the window the error is roughly 900 requests, which is fine for spotting a tenant sending 50,000 and useless for ranking two tenants 200 apart.
- Say what breaks when the window slides: Misra-Gries and Space-Saving are insert-only and cannot be decremented as records age out. The workable construction is one summary per sub-window, say ten seconds, with 30 summaries merged at query time, and the merged error is the sum of the per-summary errors, so the bound degrades linearly in the number of sub-windows.
Follow-up
- The heaviest tenant is heavy because of one export job rather than user traffic. Should the limiter treat those as the same tenant?
- Two tenants sit tied at the boundary of the top 50. Does your answer flap, and does the flapping matter?
Archive a resource graph without breaking live references or recursing
Resources reference other resources within a tenant; for the largest tenant the reference table holds up to 2,000,000 nodes and 8,000,000 edges. Archiving a resource must archive everything reachable from it that nothing outside the set still references, refuse when a live external referrer exists, and terminate when references form cycles, which they legitimately do. Produce the archive order and the refusal list, targeting O(V+E). Say what stops the traversal crossing a tenant boundary, and why recursion is the wrong control structure at this size.
Approach
- Load the subgraph with the tenant predicate on both endpoints of the edge, not only on the side you started from. Scoping the left table alone is the classic cross-tenant leak: one mis-entered edge then pulls another tenant's resources into the traversal and, worse, into the archive.
- Traverse iteratively with an explicit stack. A 2,000,000-node graph can hold a chain deep enough to exhaust a native stack in the low tens of thousands of frames, and that failure is a process crash rather than an error you can return.
- Treat cycles as data rather than corruption: compute strongly connected components with Tarjan in O(V+E) using its own explicit stack, then condense. The condensation is a DAG, so a topological order over it gives the archive order, and every member of a component archives in one transaction because no order within a cycle is valid.
- Decide refusals with reverse edges. A candidate is archivable only if every in-edge originates inside the candidate set, so build the transpose or count in-degrees restricted to the visited set, and emit each blocked resource with the id of the external referrer, which is the only part of the answer an operator can act on.
Follow-up
- The graph is read in one query and the archive writes a minute later. What can change in between, and how do you make the write safe?
- The candidate set is 400,000 resources. Is that one transaction, and if not, what does a half-finished archive look like to a reader?
Canonicalise a request body into a stable idempotency fingerprint
idempotency_key.request_fingerprint is a SHA-256 over the method, path and canonicalised body, and a retry whose fingerprint differs must be rejected with 422 rather than served the stored response. Write the canonicaliser. Bodies are JSON up to 256 KB nested at most 32 levels; clients vary key order, whitespace and unicode escaping, and some send 64-bit ids as JSON numbers. Produce a deterministic byte string such that semantically identical bodies match and any semantic difference does not. State your complexity and name two normalisations you refuse to perform.
Approach
- Parse once into a tree, then re-serialise under fixed rules: object keys sorted, array order preserved, one escaping convention, no insignificant whitespace. Parsing is O(n) and sorting keys is O(k log k) per object, so O(n log n) overall with O(depth) stack, and the 32-level cap is enforced during parsing because hostile nesting is how a canonicaliser becomes a stack overflow.
- Sort keys by their UTF-8 bytes and say why the obvious implementation is wrong in some runtimes: a default string comparison that orders by UTF-16 code units places surrogate pairs, meaning code points from U+10000 up, below U+E000 to U+FFFF, which is not UTF-8 byte order, so two services written in different languages disagree on the same document.
- Do not re-encode numbers through a double. IEEE-754 binary64 represents integers exactly only up to 2^53, so normalising a 19-digit id through a float changes it, and 1 against 1.0 cannot be reconciled without deciding whether they are the same value. Preserve the literal token, and require ids as strings at the API boundary if you want them comparable.
- Reject duplicate keys rather than picking one. JSON permits them and parsers disagree, most keeping the last, so any choice you make ties the fingerprint to a parser detail that the code handling the request does not necessarily share.
Follow-up
- A client sends the same logical request with an extra field your API ignores. Same key, different fingerprint, so you return 422. Is that the right answer?
- Where does the fingerprint get computed relative to request decompression and the body-size limit?
Denormalise tenant onto revisions and backfill it live
resource_revision (revision_id, resource_id, version, actor_user_id, change_kind, patch, request_id, created_at) has 400M rows and no tenant column; tenant_id lives only on resource. Two reads need it: a tenant-scoped audit feed ordered by created_at DESC, and an offboarding purge. Both join back to resource today. Justify adding tenant_id to resource_revision against those two reads, name the anomaly the copy introduces and the constraint that prevents it, then give the ordered migration for a live table taking 1.2k writes/second — the lock each step takes, how the backfill is batched, and where each step stops being reversible. PostgreSQL 16.
Approach
- Justify from the access path rather than from taste. Without the column, the audit feed either scans resource_revision by created_at and discards other tenants' rows, or resolves the tenant's resource_ids first and probes with them — both proportional to the tenant's whole history rather than to one page. With (tenant_id, created_at DESC, revision_id DESC) it is a seek that stops at 50 rows, and the purge becomes a ranged delete instead of a join.
- Name the cost exactly: a second copy of a fact can disagree with the first. Make the disagreement unwritable rather than documented — add UNIQUE (resource_id, tenant_id) on resource so it can serve as a foreign-key target, then FOREIGN KEY (resource_id, tenant_id) REFERENCES resource (resource_id, tenant_id) on the revision table. A revision can then only ever carry its parent's tenant.
- Step one, expand: ALTER TABLE resource_revision ADD COLUMN tenant_id BIGINT NULL, with no default, so it is a catalogue change and no rewrite. It still needs ACCESS EXCLUSIVE for an instant, and that instant queues behind the longest open transaction on the table while every later query queues behind it — set lock_timeout to 2s and retry rather than wait.
- Step two, dual-write: deploy the writer that populates tenant_id on every new revision while reads still use the join. Reversible by redeploying the previous build, because nothing reads the column yet.
Follow-up
- The backfill is half finished and a rollback is required. What state is the table in, and what does the previous build do with a half-populated column?
- How do you verify the backfill actually finished, given rows are still being inserted while it runs?
Find version gaps and relay lag with window functions
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?
Walk me through a complex software project on your resume where you had to interface with physical hardware or
Walk me through a complex software project on your resume where you had to interface with physical hardware or strict testing constraints.
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?
What is your approach to documenting your code and ensuring it can be easily audited or validated by quality a
What is your approach to documenting your code and ensuring it can be easily audited or validated by quality assurance teams?
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 would you design a software-controlled testing rig to validate the mechanical reliability of a surgical st
How would you design a software-controlled testing rig to validate the mechanical reliability of a surgical stapler?
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?
What programming languages and frameworks are you most comfortable using when building internal automation too
What programming languages and frameworks are you most comfortable using when building internal automation tools?
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?
Explain how you would approach writing a test suite for a system that has both software and hardware dependenc
Explain how you would approach writing a test suite for a system that has both software and hardware dependencies.
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 balance the need for rapid software development with the slow, deliberate pace of hardware validati
How do you balance the need for rapid software development with the slow, deliberate pace of hardware validation?
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?
Tell me about a time you had to debug a system failure where the root cause was unclear. How did you isolate t
Tell me about a time you had to debug a system failure where the root cause was unclear. How did you isolate the issue?
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?
Built from the rounds and topics Lexington Medical candidates report.
Prepare, practise & reflect
One practical outcome each day. Spend longer where you need it.
0 / 7 done01Map the Lexington Medical loop
- Write out the reported sequence: Introductory Call, Onsite Visit, Technical Discussion, Quality Session, Strategic Vision Conversation.
- 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 5 reported rounds, with the weakest marked.
02Work Software Engineering (General)
- Spend the session on Software Engineering (General), which Lexington Medical candidates report being tested on.
- Write one worked example in Software Engineering (General) and time yourself on it.
Deliverable: One timed worked example in Software Engineering (General).
03Work Technical Interviewing
- Spend the session on Technical Interviewing, which Lexington Medical 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.
04Work Product Engineering Collaboration
- Spend the session on Product Engineering Collaboration, which Lexington Medical candidates report being tested on.
- Write one worked example in Product Engineering Collaboration and time yourself on it.
Deliverable: One timed worked example in Product Engineering Collaboration.
05Answer out loud: Resume & Domain Experience
- Answer aloud, timed: Walk me through a complex software project on your resume where you had to interface with physical hardware or strict testing constraints.
- Answer aloud, timed: Describe your experience working in a regulated environment or adhering to strict quality management standards.
Deliverable: Spoken answers to 2 reported Resume & Domain Experience question(s), under time.
06Answer out loud: Technical & Product Engineering
- Answer aloud, timed: How would you design a software-controlled testing rig to validate the mechanical reliability of a surgical stapler?
- Answer aloud, timed: What programming languages and frameworks are you most comfortable using when building internal automation tools?
Deliverable: Spoken answers to 2 reported Technical & Product Engineering question(s), under time.
07Answer out loud: Product Vision & Leadership
- Answer aloud, timed: Why are you interested in working in the medical device space, and what do you think makes software engineering unique in this industry?
- Answer aloud, timed: How do you handle disagreements with hardware engineers or quality managers when defining product requirements?
Deliverable: Spoken answers to 2 reported Product Vision & Leadership question(s), under time.
Expand any day for tasks and deliverables. Your progress is saved on this device.
Behavioural rounds judge the decision you made and what it cost.
Describe your experience working in a regulated environment or adhering to strict quality management standards
Describe your experience working in a regulated environment or adhering to strict quality management standards.
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?
Why are you interested in working in the medical device space, and what do you think makes software engineerin
Why are you interested in working in the medical device space, and what do you think makes software engineering unique in this industry?
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?
How do you handle disagreements with hardware engineers or quality managers when defining product requirements
How do you handle disagreements with hardware engineers or quality managers when defining product requirements?
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 when you had to make a technical trade-off to meet a tight product launch deadline.
Describe a time when you had to make a technical trade-off to meet a tight product launch deadline.
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?
How do you stay aligned with the overall product vision of a company during rapid scaling phases?
How do you stay aligned with the overall product vision of a company during rapid scaling phases?
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?
- 01
Describe your experience working in a regulated environment or adhering to strict quality management standards.
- 02
Why are you interested in working in the medical device space, and what do you think makes software engineering unique in this industry?
- 03
How do you handle disagreements with hardware engineers or quality managers when defining product requirements?
- 04
Describe a time when you had to make a technical trade-off to meet a tight product launch deadline.
How technical is the interview process for software engineers?
The process is highly technical but focuses on practical engineering rather than abstract algorithmic puzzles. You will be evaluated on your ability to write clean, functional code, design test frameworks, and understand how your software interacts with physical systems.
Lexington Medical Software Engineer candidate reports ↗What should I expect during the facility tour?
The tour is an interactive part of the interview. It is designed to show you how the products are manufactured and tested. Use this opportunity to ask questions about the assembly process, testing setups, and how software is currently utilized on the manufacturing floor.
Lexington Medical Software Engineer candidate reports ↗How important is executive alignment in this process?
Extremely important. Because Lexington Medical maintains a flat organizational structure, you will interact with the CEO and COO. They want to see that you have strong communication skills, a clear product vision, and a genuine passion for the company's mission.
Lexington Medical Software Engineer candidate reports ↗Is there flexibility in the work location?
The role is based onsite at the facility in Bedford, MA. Because of the close integration with physical hardware, manufacturing lines, and cross-functional engineering teams, daily onsite collaboration is essential to success in this role.
Lexington Medical Software Engineer candidate reports ↗What topics does Lexington Medical test in interviews?
Lexington Medical interviews most often cover Problem Solving, Medical Device Sales, Software Engineering (General), Supply Chain Analytics, and Data Cleaning & Data Quality. The exact emphasis depends on the specific role you apply for.
Lexington Medical Software Engineer candidate reports ↗Sources & methodology 3 sources ↗
No official company page is cited. Rounds and questions come from candidate reports and PracHub editorial material; each source shows the date it was read.
- 01Lexington Medical Software Engineer candidate reports ↗
Company-reported rounds, questions and FAQ.
Candidate reports · Accessed 2026-09-22 - 02PracHub Software Engineer practice ↗
PracHub practice material, not company-reported.
PracHub page · Accessed 2026-09-22 - 03PracHub preparation framework ↗
PracHub preparation guidance.
PracHub page · Accessed 2026-09-22
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