Interview guides · ITJ

ITJ Software Engineer Interview Guide

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

The 60-second brief

As a Software Engineer at ITJ, you are a critical architect of digital transformation. You are not merely writing code; you are building scalable, high-impact solutions that bridge the gap between complex business requirements and cutting-edge technology. Your work directly influences the efficiency and technological maturity of the projects you support, often requiring you to operate in a fast-paced environment where precision and adaptability are paramount. This role requires a blend of deep technical proficiency and the ability to thrive in a collaborative, cross-functional setting. You will engage with diverse teams, including product managers and technical leads, to solve multifaceted problems.

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

Focus areas

Programming Assessments
Coding Problem Solving
Technical Interviewing

The ITJ interview process

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

Recruiter Screen

Initial screening focusing on your background, motivations, and English proficiency.

What to demonstrate

Initial screening focusing on your background, motivations, and English proficiency
Depth in Programming Assessments

How to prepare

Be able to walk your CV end to end in two minutes, and say why this company specifically.
Have your salary expectations, notice period and location constraints ready, and ask for the rest of the loop in writing.

Technical Assessments

Involves coding challenges to evaluate technical skills.

What to demonstrate

Involves coding challenges to evaluate technical skills
Depth in Programming Assessments

How to prepare

Answer aloud and timed: How do you handle edge cases when designing a new feature?
Answer aloud and timed: Can you explain the trade-offs between using different data structures for a specific problem?

Interviews with Leads

Interviews with technical leads or management to assess fit and skills.

What to demonstrate

Interviews with technical leads or management to assess fit and skills
Depth in Programming Assessments

How to prepare

Answer aloud and timed: What is your process for performing code reviews to ensure high quality and security?
Answer aloud and timed: Tell me about a time you had a disagreement with a team member; how did you resolve it?

Where candidates lose points

Communicate your thought process

Even if you don't know the exact answer, explain how you would find it.

Research the company

Understand the types of services ITJ provides to better align your answers with their business goals.

Prepare your own questions

Always have 2–3 insightful questions ready for the interviewer to show your interest.

Master the fundamentals

Many candidates focus too much on frameworks and forget the underlying data structures.

Questions & practice

How do you approach optimizing a function that is experiencing latency issues?

Medium · Technical Proficiency and Problem Solvin

Approach

Restate the input: its shape, its size, and what is guaranteed about it.
Name the brute-force solution and its complexity before improving on it.
Choose the data structure from the access pattern, not from familiarity.
State the target complexity and say which constraint rules the naive version out.

Follow-up

How does this change if the input no longer fits in memory?
What is the worst case, and how likely is it on real data?

Can you explain the trade-offs between using different data structures for a specific problem?

Medium · Technical Proficiency and Problem Solvin

Approach

Restate the input: its shape, its size, and what is guaranteed about it.
Name the brute-force solution and its complexity before improving on it.
Choose the data structure from the access pattern, not from familiarity.
State the target complexity and say which constraint rules the naive version out.

Follow-up

How does this change if the input no longer fits in memory?
What is the worst case, and how likely is it on real data?

Could you walk me through your most challenging technical project to date?

Medium · Communication and Language Skills

Approach

Say what the runtime actually does before reasoning about the code.
Name what is shared across threads and what owns each piece of state.
Identify the window where an invariant is briefly untrue.
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?

Why do you want to work at ITJ specifically?

Medium · Communication and Language Skills

Approach

Say what the runtime actually does before reasoning about the code.
Name what is shared across threads and what owns each piece of state.
Identify the window where an invariant is briefly untrue.
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?

Keep soft-deleted accounts from blocking re-registration

Easy · soft delete · unique constraints · engine differences

app_user holds user_id, tenant_id, email CITEXT, password_hash (NULL for SSO principals), email_verified_at, auth_version, status ('invited','active','suspended','deactivated'), created_at, updated_at, deleted_at. Two live accounts for one address inside a tenant must be impossible, but an address freed by a soft delete must be reusable, and the same tenant may delete and re-register it repeatedly. Write the uniqueness DDL for PostgreSQL 16, then the equivalent for MySQL 8 where partial indexes do not exist, and say what each permits once three deleted rows already hold that address.

Approach

Start from what is actually unique: not (tenant_id, email), but (tenant_id, email) among live rows. PostgreSQL says that directly — CREATE UNIQUE INDEX app_user_live_email ON app_user (tenant_id, email) WHERE deleted_at IS NULL. A full constraint over the same two columns burns the address permanently the first time someone deletes an account.
Keep case-insensitivity in the type or the index, never in the application: CITEXT as given, or UNIQUE (tenant_id, lower(email)) as an expression index where the extension is unavailable. A case-sensitive unique column is exactly how two accounts for one human appear.
For MySQL 8 the predicate has to move inside the key: add a discriminator column that is a constant 0 while the row is live and is set to user_id on delete, with UNIQUE (tenant_id, email, deleted_marker). Live rows share the constant and still collide; deleted rows differ from each other and stop colliding.
State the NULL variant and its dependency: leaving the marker NULL for deleted rows also works, because a unique index treats NULLs as distinct — true in MySQL, and true in PostgreSQL only under the default NULLS DISTINCT, which PostgreSQL 15 lets you reverse. Check the polarity against the three existing deleted rows: constant-on-live is what preserves the collision you want, and reversing it silently admits duplicate live accounts.

Follow-up

A deleted account re-registers with the same address the next day. Do the old resource rows follow the new user_id, and how does the API keep the two principals apart?
How do you honour an erasure request while resource_revision.actor_user_id still references this table?

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

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.
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.
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.
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?

How do you ensure clear communication within a remote or distributed team?

Medium · Communication and Language Skills

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?

Specify the outbound webhook contract a customer endpoint can verify

Medium · webhooks · hmac · at-least-once

Egress delivery sends resource.created, resource.updated and resource.archived to roughly 40k customer endpoints at about 1.5k deliveries/second, with a per-destination concurrency cap of 4 and a 10 second connect-plus-read timeout, at-least-once from the relay. The receiver is code you do not control, often behind a proxy that may re-encode JSON. Specify the payload envelope, how the receiver verifies authenticity and rejects replays, what ordering it may assume, how it deduplicates, which status codes it should return and what each means to us, and the retry, circuit and replay behaviour.

Approach

Send the fact, not a pointer: event_id, event_type, aggregate_type, aggregate_id, aggregate_version, occurred_at and the payload copied from outbox_event. A receiver told only that resource 42 changed has to call back, and the call back returns a newer state than the event describes - that is precisely how a consumer applies changes out of order while believing it is following them.
Sign the exact bytes on the wire: HMAC-SHA256 over the timestamp, a separator, and the raw body, in a header, compared in constant time before the body is parsed. Instruct receivers to verify the raw bytes, never a re-serialised copy, since a proxy that reorders keys or changes whitespace invalidates a signature computed over re-encoded JSON. Reject a timestamp outside a tolerance - five minutes is typical - and keep a short seen-set of event_ids, because a capture replayed inside the tolerance still verifies.
Support key rotation by sending several signature values in one header during the overlap window and publishing that any one that verifies is sufficient. Without that rule a key rotation is a synchronised outage across every destination at once.
State the guarantee as it actually is: at-least-once and unordered, including within a single aggregate_id. The outbox is ordered per aggregate at the source, but the relay holds up to 4 requests in flight per destination and backs off each retry independently, so a version 6 delivery that needs one retry lands after a version 7 that succeeded on its first attempt. Publishing per-aggregate ordering we do not enforce is worse than publishing none, because a receiver that trusts it overwrites new state with old. Receivers deduplicate on event_id and apply conditionally - UPDATE ... WHERE aggregate_version < :incoming, or the same comparison under a row lock on the aggregate - which discards stale redeliveries and stays correct when two deliveries for one aggregate are processed at the same time. A duplicate and an out-of-order delivery then have the same outcome: no-op.

Follow-up

A customer insists an event never arrived. What do you check, in order, and which table settles the argument?
A receiver cannot store a version and asks us to deliver their events in order. What would the relay have to give up to offer that, and what does one failing event then do to the rest of their stream?

Describe a time you had to debug a complex production issue under pressure.

Medium · Technical Proficiency and Problem Solvin

Approach

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

Follow-up

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

Suggested practice checklist

Built from the rounds and topics ITJ candidates report.

Day 1 — Map the ITJ loop

Write out the reported sequence: Recruiter Screen, Technical Assessments, Interviews with Leads.
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 3 reported rounds, with the weakest marked.

Day 2 — Work Programming Assessments

Spend the session on Programming Assessments, which ITJ candidates report being tested on.
Write one worked example in Programming Assessments and time yourself on it.

Deliverable: One timed worked example in Programming Assessments.

Day 3 — Work Coding Problem Solving

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

Deliverable: One timed worked example in Coding Problem Solving.

Day 4 — Work Technical Interviewing

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

Deliverable: One timed worked example in Technical Interviewing.

Day 5 — Answer out loud: Technical Proficiency and Problem Solving

Answer aloud, timed: How do you approach optimizing a function that is experiencing latency issues?
Answer aloud, timed: Describe a time you had to debug a complex production issue under pressure.

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

Day 6 — Answer out loud: Behavioral and Leadership

Answer aloud, timed: Tell me about a time you had a disagreement with a team member; how did you resolve it?
Answer aloud, timed: How do you manage your time when working on multiple high-priority tasks?

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

Day 7 — Answer out loud: Communication and Language Skills

Answer aloud, timed: Could you walk me through your most challenging technical project to date?
Answer aloud, timed: How do you ensure clear communication within a remote or distributed team?

Deliverable: Spoken answers to 2 reported Communication and Language Skills question(s), under time.

Behavioural preparation

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

How do you handle edge cases when designing a new feature?

Medium · Technical Proficiency and Problem Solvin

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?

What is your process for performing code reviews to ensure high quality and security?

Medium · Technical Proficiency and Problem Solvin

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?