cswork / libraryOpen practice workspace

Interview guides · Heliosx Group

Heliosx Group Software Engineer Interview Guide

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

The 60-second brief

A Software Engineer at Heliosx Group plays a vital role in redefining the digital healthcare landscape. As a fast-growing medtech and e-commerce scale-up behind prominent brands like Dermatica and MedExpress, the company relies on its engineering team to build scalable, secure, and highly performant platforms. You will be responsible for creating seamless user experiences, optimizing backend subscription engines, and ensuring that clinical consultation workflows are both frictionless for patients and compliant with healthcare regulations. The engineering team at Heliosx Group operates in a high-impact, fast-paced environment where software directly influences patient outcomes.

This guide is scoped to a Software Engineer candidate at Heliosx Group.

Focus areas

  • Take-home technical assessment
  • System design
  • API design (REST APIs)

The Heliosx Group interview process

Heliosx Group candidates report 5 rounds over 4-6 weeks. The stages below are what candidates describe, not a published process.

Initial Conversation

An introductory discussion to evaluate your background and fit for the role.

What to demonstrate

  • An introductory discussion to evaluate your background and fit for the role
  • Depth in Take-home technical assessment

How to prepare

  • Answer aloud and timed: How would you approach breaking down a legacy monolith application into a decoupled, microservices-based architecture?
  • Answer aloud and timed: Design a secure, scalable API endpoint for handling sensitive patient medical consultations.

Technical Evaluation

Practical, scenario-based evaluations focusing on real-world system architecture and code review.

What to demonstrate

  • Practical, scenario-based evaluations focusing on real-world system architecture and code review
  • Depth in Take-home technical assessment

How to prepare

  • Answer aloud and timed: How do you manage shared infrastructure and data consistency when scaling services across different geographical markets and distinct product lines?
  • Answer aloud and timed: What strategies would you use to handle sudden spikes in traffic on an e-commerce platform during promotional launches?

Team Collaboration Assessment

Demonstrate how you collaborate with a team through discussions and practical exercises.

What to demonstrate

  • Demonstrate how you collaborate with a team through discussions and practical exercises
  • Depth in Take-home technical assessment

How to prepare

  • Answer aloud and timed: How would you design a database schema to handle a multi-step user onboarding flow where questions dynamically change based on previous answers?
  • Answer aloud and timed: Implement a set of REST APIs in your language of choice (e.g., Java, Python) that handles user registration and medical questionnaire submissions.

Final Rounds

Concluding interviews with peer engineers, engineering leads, and executive leadership.

What to demonstrate

  • Concluding interviews with peer engineers, engineering leads, and executive leadership
  • Depth in Take-home technical assessment

How to prepare

  • Answer aloud and timed: Explain how you would optimize a multi-step React frontend form to prevent unnecessary re-renders and handle state efficiently.
  • Answer aloud and timed: Walk through your approach to writing unit and integration tests for a service that interacts with third-party payment gateways.

Offer Stage

Discussion regarding the final offer and terms of employment.

What to demonstrate

  • Discussion regarding the final offer and terms of employment
  • Depth in Take-home technical assessment

How to prepare

  • Answer aloud and timed: Given a specific code snippet from your take-home assignment, how would you refactor it to handle advanced concurrent requests?
  • Answer aloud and timed: Solve a collection-based data manipulation problem and discuss the time and space complexity of your solution.

Where candidates lose points

Over-deliver on the take-home assignment

Do not treat the take-home test as a quick draft. Structure your project professionally, include a clear README with setup instructions, write comprehensive unit tests, and implement proper error handling. This submission sets the tone for your final technical rounds.

When writing your take-home test, make sure your API design follows strict RESTful conventions

Use appropriate HTTP status codes, handle edge cases like invalid input gracefully, and ensure your database queries are optimized to prevent performance bottlenecks.

Drive the system design conversation

During the architecture round, the requirements may purposely be kept vague. Do not start designing immediately. Ask clarifying questions about user scale, data retention policies, read/write ratios, and business constraints. This demonstrates that you approach engineering with a structured, analytical mindset.

Questions & practice

How do you manage shared infrastructure and data consistency when scaling services across different geographic

Medium · System Design & Architecture

How do you manage shared infrastructure and data consistency when scaling services across different geographical markets and distinct product lines?

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 how you would optimize a multi-step React frontend form to prevent unnecessary re-renders and handle s

Medium · Coding & Technical Implementation

Explain how you would optimize a multi-step React frontend form to prevent unnecessary re-renders and handle state efficiently.

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 a specific code snippet from your take-home assignment, how would you refactor it to handle advanced con

Medium · Coding & Technical Implementation

Given a specific code snippet from your take-home assignment, how would you refactor it to handle advanced concurrent requests?

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?

Solve a collection-based data manipulation problem and discuss the time and space complexity of your solution.

Medium · Coding & Technical Implementation

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?

Replace offset paging on the resource feed with keyset

Easy · keyset pagination · composite index · sort order

resource holds resource_id, tenant_id, owner_user_id, title, body_ref, version, status ('draft','active','archived','deleted'), created_at, updated_at, deleted_at, with an index on (tenant_id, status, updated_at DESC, resource_id DESC). The listing endpoint returns active resources for one tenant, newest update first, 50 per page, today with LIMIT 50 OFFSET n. Tenants reach page 400 and rows are created while they read. Write the keyset query, define what the cursor carries and how it is encoded, and say which part of the index each predicate uses. Assume PostgreSQL 16.

Approach

  1. Name the two failures separately. OFFSET 20000 makes the server produce and discard 20,000 rows, so page cost grows with depth rather than with page size. Independently, any write that changes how many rows sort above the offset moves the window between two fetches, and the direction decides which anomaly you get: an insert lands at the head of updated_at DESC and pushes already-returned rows down past the boundary, so they are returned a second time; a delete above the offset, or a row whose updated_at is bumped above the cursor, pulls rows up and one is never returned at all. Nothing in the response reveals either.
  2. Write the seek: WHERE tenant_id = $1 AND status = 'active' AND (updated_at, resource_id) < ($2, $3) ORDER BY updated_at DESC, resource_id DESC LIMIT 50. The row-value comparison is one index range rather than a disjunction, and both columns are NOT NULL, which is what makes that comparison well defined.
  3. Map each predicate onto the index: tenant_id and status are equality on the leading columns, (updated_at, resource_id) is the range, and the ORDER BY matches the index order so no Sort node appears and the scan stops after 50 rows. The DESC in the definition only matters for mixed directions — a plain ascending btree on the same columns is read backwards for this query.
  4. Put both sort columns in the cursor and nothing the client can tamper with into another tenant: base64 of (updated_at, resource_id), validated server-side, with tenant_id taken from the principal.

Follow-up

  • The client asks for 'jump to page 400'. What do you offer instead, and what does the honest version cost?
  • Sort order becomes user-selectable across four columns. How many indexes is that, and which would you refuse to add?

Hold a per-tenant active cap against concurrent creates

Hard · write skew · isolation levels · constraints

A tenant on the standard plan may hold at most 50 resources with status='active'. The create handler runs SELECT count(*) FROM resource WHERE tenant_id = $1 AND status = 'active', compares to 50, then inserts. Two creates arrive 3 ms apart on different instances and the tenant lands at 51. Name the anomaly, say whether PostgreSQL 16 READ COMMITTED or REPEATABLE READ prevents it and why, then give an implementation that holds the cap at READ COMMITTED with the exact statements. Finally, say what changes when the cap is 'at most one running export per tenant' on job_run.

Approach

  1. Name it: write skew. The two transactions read an overlapping set and write disjoint rows, so there is no row-level conflict for the engine to detect and each commit is individually legal.
  2. Rule out the levels precisely. READ COMMITTED takes a fresh snapshot per statement and takes no lock on the counted rows, so both see 49. PostgreSQL's REPEATABLE READ is snapshot isolation: it removes non-repeatable reads and phantoms within the snapshot but still admits write skew, because the anomaly is not a re-read of a changed row, it is a read of a set that a concurrent transaction invalidates. Only SERIALIZABLE closes it, by tracking the read dependency and aborting one transaction with SQLSTATE 40001 — a guarantee that exists only if the application re-runs the whole transaction from the read.
  3. Convert the set predicate into a single-row conflict: keep tenant.active_resource_count and run UPDATE tenant SET active_resource_count = active_resource_count + 1 WHERE tenant_id = $1 AND active_resource_count < 50 in the same transaction as the INSERT. Zero affected rows is the cap, returned as 409. The row lock serialises the decision at any isolation level, and contention is bounded to one tenant's row — which is also the fair-scheduling unit, unlike a global counter that would convoy every tenant behind one row.
  4. State the cost you just took on: a counter is a second source of truth that can drift, so every path that changes status must adjust it inside the same transaction, and a periodic reconciliation has to exist, with resource_revision as the authority for what the count should have been.

Follow-up

  • A resource moves from archived back to active. Which statements change, and what breaks if the counter update and the status change land in different transactions?
  • The cap becomes plan-dependent and a plan can change mid-month. Where does the number 50 live, and who reads it?

How would you approach breaking down a legacy monolith application into a decoupled, microservices-based archi

Medium · System Design & Architecture

How would you approach breaking down a legacy monolith application into a decoupled, microservices-based 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?

Design a secure, scalable API endpoint for handling sensitive patient medical consultations.

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 strategies would you use to handle sudden spikes in traffic on an e-commerce platform during promotional

Medium · System Design & Architecture

What strategies would you use to handle sudden spikes in traffic on an e-commerce platform during promotional launches?

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 design a database schema to handle a multi-step user onboarding flow where questions dynamically

Medium · System Design & Architecture

How would you design a database schema to handle a multi-step user onboarding flow where questions dynamically change based on previous answers?

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?

Implement a set of REST APIs in your language of choice (e.g., Java, Python) that handles user registration an

Medium · Coding & Technical Implementation

Implement a set of REST APIs in your language of choice (e.g., Java, Python) that handles user registration and medical questionnaire submissions.

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?

Walk through your approach to writing unit and integration tests for a service that interacts with third-party

Medium · Coding & Technical Implementation

Walk through your approach to writing unit and integration tests for a service that interacts with third-party payment gateways.

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?

Exports duplicate a row range about once a week

Hard · leases · clock skew · idempotency

Roughly once a week an export writes a file containing a duplicated range of rows. The affected job_run rows show attempt = 1, status = succeeded, one started_at, and a lease_owner naming a different host from the one whose logs show the job starting. Leases last 30 seconds and are heartbeated every 10 from inside the handler; lease_expires_at is computed on the worker and compared against the database's now(). Find the mechanism, and give a fix that holds even if you cannot fix the clocks.

Approach

  1. Start from the fact that eliminates the obvious answer. attempt = 1 means no retry was recorded, so this is not a re-run after failure; two workers ran the same row concurrently and the takeover path never touched the counter. lease_owner naming a host other than the one that started the job is the same statement from the other side.
  2. Enumerate the mechanisms that cause a premature takeover, then find the signal that separates them. Either the lease genuinely expired because the heartbeat did not fire, which is what happens when the heartbeat runs on the handler's own thread and the handler makes a long blocking call, or it only appeared expired because two clocks disagree, since lease_expires_at is written from the worker's clock and evaluated against the database's. The discriminator is the distribution: incidents clustered on the longest exports indict the heartbeat, incidents clustered on one host indict skew. Measure both, and measure each host's offset against the database directly.
  3. Read the reclaim query precisely. In PostgreSQL now() is transaction start time, not statement time, so a reclaimer holding a long transaction compares against an older timestamp than expected; clock_timestamp() is the statement-time function. This is worth ruling in or out before you redesign anything, because it changes which rows look expired.
  4. Remove the second clock rather than trying to synchronise it. Issue and extend the lease in the database, with lease_expires_at = now() + interval '30 seconds' in both the claim and the heartbeat, so exactly one clock is ever compared and worker skew stops mattering to this predicate.

Follow-up

  • The displaced worker has already streamed half the file to object storage. What makes that side effect safe to repeat?
  • You now count takeovers. What alert fires on that counter, and at what threshold?

Suggested practice checklist

Built from the rounds and topics Heliosx Group candidates report.

Day 1 — Map the Heliosx Group loop

  • Write out the reported sequence: Initial Conversation, Technical Evaluation, Team Collaboration Assessment, Final Rounds, Offer Stage.
  • 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.

Day 2 — Work Take-home technical assessment

  • Spend the session on Take-home technical assessment, which Heliosx Group candidates report being tested on.
  • Write one worked example in Take-home technical assessment and time yourself on it.

Deliverable: One timed worked example in Take-home technical assessment.

Day 3 — Work System design

  • Spend the session on System design, which Heliosx Group 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 API design (REST APIs)

  • Spend the session on API design (REST APIs), which Heliosx Group candidates report being tested on.
  • Write one worked example in API design (REST APIs) and time yourself on it.

Deliverable: One timed worked example in API design (REST APIs).

Day 5 — Answer out loud: System Design & Architecture

  • Answer aloud, timed: How would you approach breaking down a legacy monolith application into a decoupled, microservices-based architecture?
  • Answer aloud, timed: Design a secure, scalable API endpoint for handling sensitive patient medical consultations.

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

Day 6 — Answer out loud: Coding & Technical Implementation

  • Answer aloud, timed: Implement a set of REST APIs in your language of choice (e.g., Java, Python) that handles user registration and medical questionnaire submissions.
  • Answer aloud, timed: Explain how you would optimize a multi-step React frontend form to prevent unnecessary re-renders and handle state efficiently.

Deliverable: Spoken answers to 2 reported Coding & Technical Implementation question(s), under time.

Day 7 — Answer out loud: Behavioral & Cultural Alignment

  • Answer aloud, timed: Tell me about your favorite software project. What made it successful, and what would you do differently today?
  • Answer aloud, timed: Describe a time when you had to lead a project with ambiguous requirements. How did you align stakeholders and engineering resources?

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

Behavioural preparation

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

Tell me about your favorite software project. What made it successful, and what would you do differently today

Medium · Behavioral & Cultural Alignment

Tell me about your favorite software project. What made it successful, and what would you do differently today?

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?

Describe a time when you had to lead a project with ambiguous requirements. How did you align stakeholders and

Medium · Behavioral & Cultural Alignment

Describe a time when you had to lead a project with ambiguous requirements. How did you align stakeholders and engineering resources?

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?

Why do you want to work in the digital health/medtech space, and what interests you specifically about Heliosx

Medium · Behavioral & Cultural Alignment

Why do you want to work in the digital health/medtech space, and what interests you specifically about Heliosx Group?

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 handle constructive feedback on your code, especially when there are strong, differing opinions wit

Medium · Behavioral & Cultural Alignment

How do you handle constructive feedback on your code, especially when there are strong, differing opinions within the team?

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?

Describe a situation where you had to balance technical debt with the pressure to deliver a feature quickly. H

Medium · Behavioral & Cultural Alignment

Describe a situation where you had to balance technical debt with the pressure to deliver a feature quickly. How did you negotiate the trade-offs?

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?