cswork / libraryOpen practice workspace

Interview guides · NCS

NCS Software Engineer Interview Guide

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

The 60-second brief

As a Software Engineer at NCS, you are at the heart of delivering large-scale digital transformation projects that impact government, telecommunications, and financial sectors. You are not just writing code; you are building the digital backbone for critical infrastructure and enterprise-grade solutions. This role requires a balance of technical rigor and the ability to navigate complex, multi-stakeholder project environments. Your work directly influences how millions of users interact with services, requiring you to think about scalability, security, and maintainability from day one. Whether you are working on backend microservices, frontend integration, or cloud-native architecture, your contributions are essential to the delivery of high-impact systems.

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

Focus areas

  • Data Structures & Algorithms (DSA)
  • Java
  • Spring Boot

The NCS interview process

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

Application Review

Initial review of your application to assess qualifications and fit for the role.

What to demonstrate

  • Initial review of your application to assess qualifications and fit for the role
  • Depth in Data Structures & Algorithms (DSA)

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.

Screening

Initial screening to evaluate your technical foundation and cultural fit.

What to demonstrate

  • Initial screening to evaluate your technical foundation and cultural fit
  • Depth in Data Structures & Algorithms (DSA)

How to prepare

  • Answer aloud and timed: How do you optimize a slow SQL query?
  • Answer aloud and timed: Describe the core concepts of Object-Oriented Programming (OOP) and how you apply them in your code.

Technical Assessments

In-depth technical evaluations to gauge your real-world readiness and problem-solving skills.

What to demonstrate

  • In-depth technical evaluations to gauge your real-world readiness and problem-solving skills
  • Depth in Data Structures & Algorithms (DSA)

How to prepare

  • Answer aloud and timed: Explain the difference between strong, weak, and unowned references in memory management.
  • Answer aloud and timed: Can you describe a time you faced a conflict in a project and how you resolved it?

Resume Deep-Dive

Detailed discussion of your resume and project experience with interviewers.

What to demonstrate

  • Detailed discussion of your resume and project experience with interviewers
  • Depth in Data Structures & Algorithms (DSA)

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.

Behavioral Questions

Situational questions to assess your behavioral responses and cultural alignment.

What to demonstrate

  • Situational questions to assess your behavioral responses and cultural alignment
  • Depth in Data Structures & Algorithms (DSA)

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

Final Selection

Final review and decision-making process involving multiple stakeholders.

What to demonstrate

  • Final review and decision-making process involving multiple stakeholders
  • Depth in Data Structures & Algorithms (DSA)

How to prepare

  • Answer aloud and timed: Explain your thought process when troubleshooting a production issue.
  • Answer aloud and timed: How would you design a Pub-Sub system using a client-server model?

Where candidates lose points

Own your projects

Be prepared to present your school or work projects in detail. Have diagrams or code snippets ready if the interview is remote.

Understand the "Why

Don't just list technologies you used. Explain the business problem you were solving and why your chosen solution was the most effective.

Be honest about limitations

If you don't know an answer, clearly state what you know, admit the gap, and explain how you would go about finding the answer.

Prepare questions

Always have 2–3 insightful questions about the team, the project types, or the company's development programs to show your engagement.

Questions & practice

Explain the difference between strong, weak, and unowned references in memory management.

Medium · Technical & Architecture

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?

Given a specific scenario, how would you handle concurrency and reference counting?

Medium · Problem-Solving & Puzzles

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?

Canonicalise a request body into a stable idempotency fingerprint

Medium · parsing · canonicalisation · hashing

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

  1. 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.
  2. 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.
  3. 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.
  4. 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?

How do you optimize a slow SQL query?

Medium · Technical & Architecture

Approach

  1. Name the grain you start from and join outward from it.
  2. Check whether any join is one-to-many before aggregating, or the sums inflate.
  3. Say which index the query would use, and what makes it unusable.
  4. Handle the rows that do not match: that is usually the actual question.

Follow-up

  • How does the query change if that join becomes one-to-many?
  • What happens to this when the table is ten times larger?

Why do you want to join NCS, and what draws you to this specific role?

Medium · Behavioral & Leadership

Approach

  1. Name the grain you start from and join outward from it.
  2. Check whether any join is one-to-many before aggregating, or the sums inflate.
  3. Say which index the query would use, and what makes it unusable.
  4. Handle the rows that do not match: that is usually the actual question.

Follow-up

  • How does the query change if that join becomes one-to-many?
  • What happens to this when the table is ten times larger?

How would you design a RESTful service for a booking system?

Medium · Technical & 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?

Explain the difference between microservices and monolithic architectures.

Medium · Technical & 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?

Describe the core concepts of Object-Oriented Programming (OOP) and how you apply them in your code.

Medium · Technical & Architecture

Approach

  1. Fix the scope first: who calls this, how often, and what they do when it fails.
  2. Name the read and write paths separately; they rarely have the same bottleneck.
  3. Choose a partition key and say what query it makes expensive.
  4. State the consistency you need, and where you are willing to be stale.

Follow-up

  • What breaks first when traffic grows ten times?
  • How does this behave when that dependency is down for an hour?

How would you design a Pub-Sub system using a client-server model?

Medium · Problem-Solving & Puzzles

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?

Explain your thought process when troubleshooting a production issue.

Medium · Problem-Solving & Puzzles

Approach

  1. Establish what changed and when, before forming any theory.
  2. Pick a bisection that eliminates candidates whichever way it turns out.
  3. Check the instrumentation before believing the symptom.
  4. Separate the trigger from the cause; the deploy is rarely the bug.

Follow-up

  • What would you look at first, and what would it rule out?
  • How would you tell a cause from a coincidence here?

Suggested practice checklist

Built from the rounds and topics NCS candidates report.

Day 1 — Map the NCS loop

  • Write out the reported sequence: Application Review, Screening, Technical Assessments, Resume Deep-Dive, Behavioral Questions, Final Selection.
  • 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 Data Structures & Algorithms (DSA)

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

Deliverable: One timed worked example in Data Structures & Algorithms (DSA).

Day 3 — Work Java

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

Deliverable: One timed worked example in Java.

Day 4 — Work Spring Boot

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

Deliverable: One timed worked example in Spring Boot.

Day 5 — Answer out loud: Technical & Architecture

  • Answer aloud, timed: How would you design a RESTful service for a booking system?
  • Answer aloud, timed: Explain the difference between microservices and monolithic architectures.

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

Day 6 — Answer out loud: Behavioral & Leadership

  • Answer aloud, timed: Can you describe a time you faced a conflict in a project and how you resolved it?
  • Answer aloud, timed: Why do you want to join NCS, and what draws you to this specific role?

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

Day 7 — Answer out loud: Problem-Solving & Puzzles

  • Answer aloud, timed: Explain your thought process when troubleshooting a production issue.
  • Answer aloud, timed: How would you design a Pub-Sub system using a client-server model?

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

Behavioural preparation

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

Can you describe a time you faced a conflict in a project and how you resolved it?

Medium · Behavioral & Leadership

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?

How do you handle tight deadlines and competing stakeholder requirements?

Medium · Behavioral & Leadership

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?

Tell me about a project you are particularly proud of and your specific contribution to it.

Medium · Behavioral & Leadership

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?

How do you approach learning new technologies when faced with a project requirement you are unfamiliar with?

Medium · Behavioral & Leadership

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?