Interview guides · Belt Power

Belt Power Software Engineer Interview Guide

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

The 60-second brief

As a Software Engineer at Belt Power, you will play a vital role in delivering innovative software solutions that drive efficiency and effectiveness across the organization. This position is integral to the development of systems that support our mission of providing superior products and services in the power transmission and conveyor industry. Your contributions will impact both internal processes and the user experience, ensuring that our offerings remain competitive and reliable. In this role, you will engage with complex challenges, developing scalable solutions that not only meet the needs of our clients but also enhance our operational capabilities. You will collaborate with cross-functional teams, including product management and operations, to create software that optimally integrates with our existing infrastructure.

This guide is scoped to a Software Engineer candidate at Belt Power.

Focus areas

C#
.NET
T-SQL

The Belt Power interview process

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

Initial Screening

Candidates undergo a preliminary review to assess qualifications and fit for the role.

What to demonstrate

Candidates undergo a preliminary review to assess qualifications and fit for the role
Depth in C#

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

Candidates participate in technical interviews that evaluate coding skills and problem-solving abilities.

What to demonstrate

Candidates participate in technical interviews that evaluate coding skills and problem-solving abilities
Depth in C#

How to prepare

Answer aloud and timed: How do you ensure the quality of the code you write?
Answer aloud and timed: Can you explain the differences between REST and SOAP APIs?

Behavioral Interviews

Interviews focus on interpersonal skills, teamwork, and leadership experiences.

What to demonstrate

Interviews focus on interpersonal skills, teamwork, and leadership experiences
Depth in C#

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

Coding Challenge

Candidates may complete a practical coding challenge to demonstrate their programming skills.

What to demonstrate

Candidates may complete a practical coding challenge to demonstrate their programming skills
Depth in C#

How to prepare

Answer aloud and timed: How would you approach scaling an application to handle increased load?
Answer aloud and timed: What factors do you consider when selecting a database for a new application?

Final Interviews

Candidates engage in final discussions with team members to assess cultural fit and alignment with company values.

What to demonstrate

Candidates engage in final discussions with team members to assess cultural fit and alignment with company values
Depth in C#

How to prepare

Answer aloud and timed: Describe a microservices architecture and its benefits.
Answer aloud and timed: How do you handle data consistency in distributed systems?

Offer Discussion

Successful candidates receive an offer and discuss terms of employment.

What to demonstrate

Successful candidates receive an offer and discuss terms of employment
Depth in C#

How to prepare

Answer aloud and timed: Describe a time when you had a conflict with a team member and how you resolved it.
Answer aloud and timed: How do you prioritize tasks when managing multiple projects?

Where candidates lose points

Going into the loop without having done this.

Practice Coding: Regularly engage in coding challenges on platforms like LeetCode or HackerRank to sharpen your skills.

Going into the loop without having done this.

Understand Company Values: Familiarize yourself with Belt Power's mission and values, as alignment is crucial for cultural fit.

Going into the loop without having done this.

Prepare Real-world Examples: Be ready to share specific examples from your experience that demonstrate your skills and problem-solving abilities.

Going into the loop without having done this.

Ask Questions: Prepare thoughtful questions to ask your interviewers, reflecting your interest in the role and company.

Going into the loop without having done this.

Be Yourself: Authenticity is valued at Belt Power. Share your genuine perspectives and experiences during the interview.

Questions & practice

Write a function to reverse a string in your preferred programming language.

Medium · Coding / Algorithms

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?

How would you implement a binary search algorithm?

Medium · Coding / Algorithms

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?

Given a list of integers, find the two numbers that add up to a specific target.

Medium · Coding / Algorithms

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?

Explain the time complexity of your proposed solutions.

Medium · Coding / Algorithms

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?

Demonstrate how you would use data structures to solve a specific problem.

Medium · Coding / Algorithms

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?

Denormalise tenant onto revisions and backfill it live

Hard · denormalisation · online migration · backfill

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?

Write the update path that detects a concurrent edit

Medium · optimistic concurrency · transactional outbox · audit history

resource carries version INT NOT NULL DEFAULT 1. resource_revision holds revision_id, resource_id, version, actor_user_id, change_kind, patch JSONB, request_id, created_at with UNIQUE (resource_id, version). outbox_event holds aggregate_type, aggregate_id, aggregate_version, event_type, payload, status. A PUT carries the version the client read. Write the exact statements for the single transaction that applies the edit, records the revision and enqueues 'resource.updated', and give the handler's branch on zero affected rows. Then say what PostgreSQL 16 does under READ COMMITTED when two of these updates hit one row at once.

Approach

One transaction, three writes, no network call inside it: UPDATE resource SET title = $3, version = version + 1, updated_at = now() WHERE resource_id = $1 AND tenant_id = $4 AND version = $2; then INSERT the resource_revision row at version $2 + 1; then INSERT the outbox_event row at the same aggregate_version. The event goes to a table rather than a broker because no transaction spans both.
Branch on the affected-row count before doing anything else. Zero has three causes — stale version, wrong tenant, row gone — so re-read once and map to 409 carrying the current version, or 404 for an id outside the caller's tenant, which also stops the endpoint confirming that another tenant's id exists.
State the engine behaviour instead of assuming it. Under READ COMMITTED the second UPDATE blocks on the row lock, and when the first commits PostgreSQL re-evaluates the WHERE clause against the newly committed row, so the version predicate now fails and the statement reports zero rows. Under REPEATABLE READ the identical collision raises SQLSTATE 40001 instead, so the handler must fold both shapes into one conflict response.
Keep UNIQUE (resource_id, version) even though the predicate already serialises writers. It is what makes a lost update unwritable if any other path ever reaches the revision table, and it converts a logic bug into 23505 rather than into a silently missing history row.

Follow-up

A client sends the version it read ten minutes ago and the resource has moved three versions. What is in your 409 so it can resolve the conflict without a full re-fetch?
Two editors, two disjoint fields, no overlap. Does your answer still refuse the second write, and should it?