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HKT Services Software Engineer Interview Guide

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

The 60-second brief

As a Software Engineer at HKT Services, you are at the heart of Hong Kong’s telecommunications and digital infrastructure. You are responsible for designing, building, and maintaining the robust systems that power everything from enterprise-grade networking solutions to consumer-facing digital platforms. Your work directly impacts millions of users, requiring a balance between high-performance engineering and the reliability expected of a market-leading service provider. This role is both technically demanding and strategically significant. You will collaborate across departments to translate complex business requirements into scalable code, often working within a large-scale, enterprise environment.

This guide is scoped to a Software Engineer candidate at HKT Services.

Focus areas

  • Java
  • Project/Portfolio Communication (FYP & site project demo)
  • English Communication (speaking & writing)

The HKT Services interview process

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

Written Assessments

Initial tests to evaluate baseline knowledge through written tests or coding assessments.

What to demonstrate

  • Initial tests to evaluate baseline knowledge through written tests or coding assessments
  • Depth in Java

How to prepare

  • Answer aloud and timed: How would you handle a production-level edge case in a high-traffic system?
  • Answer aloud and timed: Explain your experience with RESTful APIs and their application in your past projects.

Technical Discussions

Face-to-face or virtual interactions with managers and senior engineers to discuss technical skills.

What to demonstrate

  • Face-to-face or virtual interactions with managers and senior engineers to discuss technical skills
  • Depth in Java

How to prepare

  • Answer aloud and timed: Describe the internal workings of Java Collections or your preferred language's memory management.
  • Answer aloud and timed: What is your experience with Linux shell scripting or automation?

Group Exercises

Collaborative tasks designed to assess teamwork and problem-solving abilities.

What to demonstrate

  • Collaborative tasks designed to assess teamwork and problem-solving abilities
  • Depth in Java

How to prepare

  • Answer aloud and timed: How do you ensure code quality and maintainability in large-scale projects?
  • Answer aloud and timed: Walk us through a technical challenge you faced in a recent project and how you resolved it.

Final Interviews

Behavioral and technical interviews to evaluate overall fit and project presentation skills.

What to demonstrate

  • Behavioral and technical interviews to evaluate overall fit and project presentation skills
  • Depth in Java

How to prepare

  • Answer aloud and timed: Why did you choose specific technologies for your project, and how do they compare to alternatives?
  • Answer aloud and timed: How do you collaborate with team members when you encounter conflicting technical opinions?

Where candidates lose points

Master your project details

Be ready to defend every technical choice you made in your FYP or previous work.

Practice your English and Cantonese

Depending on the team, you may be interviewed in either or both. Being comfortable in both is a significant advantage.

Stay current with industry trends

Knowledge of current developments in the networking and IT sector will help you stand out during group discussions.

Ask thoughtful questions

Use the interview as an opportunity to learn about the team’s current tech stack and the challenges they face.

Questions & practice

Describe the internal workings of Java Collections or your preferred language's memory management.

Medium · Technical & Domain Knowledge

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?

Walk us through a technical challenge you faced in a recent project and how you resolved it.

Medium · Project Experience & Problem Solving

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?

Why did you choose specific technologies for your project, and how do they compare to alternatives?

Medium · Project Experience & Problem Solving

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?

Explain why the owner filter ignores the listing index

Medium · composite index · query plans · sort elimination

The only index on resource is (tenant_id, status, updated_at DESC, resource_id DESC). A new endpoint returns one user's resources across all statuses, newest created first: WHERE tenant_id = $1 AND owner_user_id = $2 ORDER BY created_at DESC LIMIT 20. On a tenant with 2M rows it takes 900 ms and EXPLAIN shows a sort above a large scan. Explain precisely why the existing index cannot serve it, give the index that can, and state which of these the new index still will not help: owner_user_id alone across tenants; the same query ordered by updated_at. PostgreSQL 16.

Approach

  1. Separate the two jobs an index does. For filtering, a composite btree is seekable only on a left prefix, so with no predicate on status the scan can at best range over tenant_id and test owner_user_id per row; PostgreSQL 16 has no btree skip scan to jump the unconstrained column.
  2. For ordering, the index is sorted by (status, updated_at) within a tenant and not by created_at, so the LIMIT cannot stop early: every matching row is read and then sorted. That is the 'Sort Method: top-N heapsort' line, and it is why the plan reads 2M rows to answer with 20.
  3. Derive the replacement from the access path — equality, equality, then the ordering column: CREATE INDEX CONCURRENTLY ON resource (tenant_id, owner_user_id, created_at DESC). The scan seeks to the (tenant, owner) range and walks 20 entries in order, so the Sort node disappears along with the row-read.
  4. Treat INCLUDE (title, status) as conditional, not free. An index-only scan still visits the heap for any row whose page is not marked all-visible, so on a table taking 1.2k writes/second the win depends on autovacuum keeping the visibility map current, and the wider index costs more on every insert.

Follow-up

  • 90% of rows are status='active'. Would a partial index WHERE status = 'active' change your answer, and for which of the three queries?
  • A dashboard runs this for 40 owners in one page load. What changes about the design?

How would you handle a production-level edge case in a high-traffic system?

Medium · Technical & Domain Knowledge

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 do you ensure code quality and maintainability in large-scale projects?

Medium · Technical & Domain Knowledge

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?

One log partition stops advancing while the others drain

Easy · poison message · head-of-line blocking · consumer lag

Search results for a subset of tenants are hours stale; the rest are current. The projection consumer reports lag of zero on 15 of 16 partitions and 400,000 on one. Its error rate is flat and its CPU is idle. outbox_event has no pending rows older than a second, so the relay has published everything it holds. Identify the mechanism, give the ordered checks, and state what you do in the first ten minutes versus what you change permanently.

Approach

  1. Read the lag distribution first. A slow consumer lags everywhere; zero on fifteen partitions and 400,000 on one is not throughput. Idle CPU on the stuck partition means the consumer is not advancing its offset at all, which points at one message it cannot get past rather than at a rate problem.
  2. Exonerate the producer before touching the consumer. No pending outbox rows older than a second means the relay published, so the event exists in the log. This separates never sent from sent and never applied, which are different code paths and usually different owners.
  3. Read the message at the stuck offset and the handler's log lines for its event_id. A flat error rate with no progress has two explanations and you must distinguish them: the handler is throwing and the retry loop is swallowing it, or the handler is blocking on something and never returning. Idle CPU with no error lines favours the second.
  4. Mitigate before diagnosing further. Move the offending event to a dead-letter store and commit the offset past it. Adding consumers does nothing here, because a partition is consumed by exactly one member of the group, and the blast radius is every aggregate hashed to that partition, not only the aggregate that produced the bad event.

Follow-up

  • The dead-lettered event carried aggregate_version 7 and the projection had applied 6. What must the replay do differently if 8 and 9 landed in the meantime?
  • How do you show staleness to the user while the partition is behind, given the API already returns the projection's watermark?

Suggested practice checklist

Built from the rounds and topics HKT Services candidates report.

Day 1 — Map the HKT Services loop

  • Write out the reported sequence: Written Assessments, Technical Discussions, Group Exercises, Final 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 Java

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

Deliverable: One timed worked example in Java.

Day 3 — Work Project/Portfolio Communication (FYP & site project demo)

  • Spend the session on Project/Portfolio Communication (FYP & site project demo), which HKT Services candidates report being tested on.
  • Write one worked example in Project/Portfolio Communication (FYP & site project demo) and time yourself on it.

Deliverable: One timed worked example in Project/Portfolio Communication (FYP & site project demo).

Day 4 — Work English Communication (speaking & writing)

  • Spend the session on English Communication (speaking & writing), which HKT Services candidates report being tested on.
  • Write one worked example in English Communication (speaking & writing) and time yourself on it.

Deliverable: One timed worked example in English Communication (speaking & writing).

Day 5 — Answer out loud: Technical & Domain Knowledge

  • Answer aloud, timed: How would you handle a production-level edge case in a high-traffic system?
  • Answer aloud, timed: Explain your experience with RESTful APIs and their application in your past projects.

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

Day 6 — Answer out loud: Project Experience & Problem Solving

  • Answer aloud, timed: Walk us through a technical challenge you faced in a recent project and how you resolved it.
  • Answer aloud, timed: Why did you choose specific technologies for your project, and how do they compare to alternatives?

Deliverable: Spoken answers to 2 reported Project Experience & Problem Solving question(s), under time.

Day 7 — Answer out loud: Behavioral & Situational

  • Answer aloud, timed: Tell us about a time you had to explain a complex technical concept to a non-technical stakeholder.
  • Answer aloud, timed: How do you handle pressure or tight deadlines when working on a critical system?

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

Behavioural preparation

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

Explain your experience with RESTful APIs and their application in your past projects.

Medium · Technical & Domain Knowledge

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?

What is your experience with Linux shell scripting or automation?

Medium · Technical & Domain Knowledge

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 collaborate with team members when you encounter conflicting technical opinions?

Medium · Project Experience & Problem Solving

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

Medium · Project Experience & Problem Solving

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 project requirements that change mid-development?

Medium · Project Experience & Problem Solving

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 us about a time you had to explain a complex technical concept to a non-technical stakeholder.

Medium · Behavioral & Situational

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 pressure or tight deadlines when working on a critical system?

Medium · Behavioral & Situational

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?

What interests you about the telecommunications and IT sector in Hong Kong?

Medium · Behavioral & Situational

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 approach learning new technologies or frameworks on the job?

Medium · Behavioral & Situational

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?