cswork / libraryOpen practice workspace

Interview guides · Fast Enterprises

Fast Enterprises Software Engineer Interview Guide

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

The 60-second brief

A Software Engineer at Fast Enterprises plays a pivotal role in developing and maintaining software solutions that enhance the efficiency and effectiveness of government agencies and businesses. This position is crucial as it directly impacts the quality of services provided to users and the overall success of the company’s projects. As a Software Engineer, you will work on complex systems that require a deep understanding of user needs, technical architecture, and software development best practices. The role offers the opportunity to engage with various teams and technologies, taking part in projects that contribute to significant improvements in public service delivery. You will collaborate with cross-functional teams, including product management, quality assurance, and client support, to ensure that the software solutions are robust, scalable, and user-friendly.

This guide is scoped to a Software Engineer candidate at Fast Enterprises.

Focus areas

  • Behavioral / HR interviewing
  • Logic and reasoning quizzes
  • Pseudocode problem solving

The Fast Enterprises interview process

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

Initial Screening

The process begins with an initial screening by an HR representative to assess basic qualifications.

What to demonstrate

  • The process begins with an initial screening by an HR representative to assess basic qualifications
  • Depth in Behavioral / HR interviewing

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 undergo technical assessments to evaluate their programming and software development skills.

What to demonstrate

  • Candidates undergo technical assessments to evaluate their programming and software development skills
  • Depth in Behavioral / HR interviewing

How to prepare

  • Answer aloud and timed: How do you ensure code quality and maintainability in your projects?
  • Answer aloud and timed: Write a function to find the first 100 prime numbers.

Coding Challenges

Practical coding challenges are administered to demonstrate coding skills and problem-solving abilities.

What to demonstrate

  • Practical coding challenges are administered to demonstrate coding skills and problem-solving abilities
  • Depth in Behavioral / HR interviewing

How to prepare

  • Answer aloud and timed: How would you optimize a sorting algorithm for large datasets?
  • Answer aloud and timed: Describe how you would implement a basic hash table.

Behavioral Interviews

Behavioral interviews assess soft skills and cultural fit within the organization.

What to demonstrate

  • Behavioral interviews assess soft skills and cultural fit within the organization
  • Depth in Behavioral / HR interviewing

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.

Final Evaluation

The interview process concludes with a final evaluation of the candidate's overall fit for the role.

What to demonstrate

  • The interview process concludes with a final evaluation of the candidate's overall fit for the role
  • Depth in Behavioral / HR interviewing

How to prepare

  • Answer aloud and timed: Describe a situation where you had to work with a difficult team member.
  • Answer aloud and timed: How would you approach debugging a complex software issue in a production environment?

Where candidates lose points

Practice Coding Problems

Regularly solve coding challenges on platforms like LeetCode to sharpen your skills.

Understand the Company Values

Familiarize yourself with Fast Enterprises' mission and values to convey alignment during your interview.

Communicate Clearly

When discussing technical concepts, aim to explain your thought process clearly, especially when tackling coding questions.

Questions & practice

Write a function to find the first 100 prime numbers.

Medium · Coding / Algorithms

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?

How would you optimize a sorting algorithm for large datasets?

Medium · Coding / Algorithms

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?

Describe how you would implement a basic hash table.

Medium · Coding / Algorithms

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?

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?

Find version gaps and relay lag with window functions

Medium · window functions · event tables · frame semantics

outbox_event holds event_id, aggregate_type, aggregate_id, aggregate_version, event_type, payload, status ('pending','published','dead'), attempts, created_at, published_at. A projection is missing rows and you must decide whether the relay skipped events or the consumer dropped them. Write three queries over the last seven days: one listing every aggregate_id whose published aggregate_version sequence has a hole, one giving per-day counts with a running total, and one returning the newest published event per aggregate. For each, say where the window function is evaluated relative to WHERE and LIMIT. PostgreSQL 16.

Approach

  1. Gaps: compute lead(aggregate_version) OVER (PARTITION BY aggregate_id ORDER BY aggregate_version) in a subquery, then filter next_version <> aggregate_version + 1 in the outer query. Window functions are evaluated after WHERE, GROUP BY and HAVING and before the outer ORDER BY and LIMIT, so the predicate cannot sit in the same WHERE clause and PostgreSQL 16 has no QUALIFY.
  2. Say what the seven-day filter does to the answer: it truncates every partition, so the first row per aggregate has no predecessor inside the window and a hole spanning the boundary is invisible. Widen the window, or join to resource.version as the authority for the true maximum.
  3. Running total: SELECT date_trunc('day', created_at) AS d, count() AS n, sum(count()) OVER (ORDER BY date_trunc('day', created_at) ROWS UNBOUNDED PRECEDING). An aggregate inside a window call is legal because grouping runs before windowing. The grouping key is unique per row here so ROWS and RANGE agree, but write the frame anyway — over ungrouped rows with tied timestamps the default RANGE frame pulls in every peer row and the total jumps.
  4. Newest per aggregate: DISTINCT ON (aggregate_id) ... ORDER BY aggregate_id, aggregate_version DESC is the cheap PostgreSQL-only form when an index matches that order; row_number() OVER (PARTITION BY aggregate_id ORDER BY aggregate_version DESC) = 1 is the portable form and needs a subquery for the same evaluation-order reason as the gap query.

Follow-up

  • Relay failover redelivers events. Does a duplicate break the gap query, and how would you detect one from this table alone?
  • Turn the gap check into a continuous monitor rather than a query someone runs after an incident. What does it watch?

What is the difference between a class and an interface in Java?

Medium · Technical / Domain Questions

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?

Can you explain the concept of inheritance and provide an example?

Medium · Technical / Domain Questions

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 your projects?

Medium · Technical / Domain Questions

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?

Describe how you would design a scalable web application.

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 considerations would you take into account when building a microservices architecture?

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?

How would you approach debugging a complex software issue in a production environment?

Medium · Problem-Solving / Case Studies

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 Fast Enterprises candidates report.

Day 1 — Map the Fast Enterprises loop

  • Write out the reported sequence: Initial Screening, Technical Assessments, Coding Challenges, Behavioral Interviews, Final Evaluation.
  • 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 Behavioral / HR interviewing

  • Spend the session on Behavioral / HR interviewing, which Fast Enterprises candidates report being tested on.
  • Write one worked example in Behavioral / HR interviewing and time yourself on it.

Deliverable: One timed worked example in Behavioral / HR interviewing.

Day 3 — Work Logic and reasoning quizzes

  • Spend the session on Logic and reasoning quizzes, which Fast Enterprises candidates report being tested on.
  • Write one worked example in Logic and reasoning quizzes and time yourself on it.

Deliverable: One timed worked example in Logic and reasoning quizzes.

Day 4 — Work Pseudocode problem solving

  • Spend the session on Pseudocode problem solving, which Fast Enterprises candidates report being tested on.
  • Write one worked example in Pseudocode problem solving and time yourself on it.

Deliverable: One timed worked example in Pseudocode problem solving.

Day 5 — Answer out loud: Technical / Domain Questions

  • Answer aloud, timed: What is the difference between a class and an interface in Java?
  • Answer aloud, timed: Can you explain the concept of inheritance and provide an example?

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

Day 6 — Answer out loud: Coding / Algorithms

  • Answer aloud, timed: Write a function to find the first 100 prime numbers.
  • Answer aloud, timed: How would you optimize a sorting algorithm for large datasets?

Deliverable: Spoken answers to 2 reported Coding / Algorithms question(s), under time.

Day 7 — Answer out loud: Behavioral / Leadership

  • Answer aloud, timed: Tell me about a time you faced a challenge in a project and how you overcame it.
  • Answer aloud, timed: How do you prioritize tasks when working on multiple projects?

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

Behavioural preparation

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

Tell me about a time you faced a challenge in a project and how you overcame 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 prioritize tasks when working on multiple projects?

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?

Describe a situation where you had to work with a difficult team member.

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?

If a client requests a feature that conflicts with existing system architecture, how would you handle the situ

Medium · Problem-Solving / Case Studies

If a client requests a feature that conflicts with existing system architecture, how would you handle the situation?

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?