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Toyon Research Software Engineer Interview Guide

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

The 60-second brief

Toyon Research is a premier national security contractor specializing in defense and aerospace technologies. As a Software Engineer, you will develop mission-critical planning, decision-support, and analysis applications for government customers, primarily the US Department of Defense. Your work will directly impact national security, utilizing complex algorithms, geographic information systems (GIS), and high-performance computing to solve real-world defense challenges. In this role, you will collaborate with multidisciplinary teams of scientists, analysts, and senior engineers to build robust software systems featuring intuitive user interfaces. Whether you are optimizing search methods, implementing numerical algorithms, or configuring cluster computing platforms, your contributions will transition advanced scientific research into operational, real-world capabilities.

This guide is scoped to a Software Engineer candidate at Toyon Research.

Focus areas

  • Object-Oriented Programming (OOP)
  • C++
  • GIS (Geographic Information Systems)

The Toyon Research interview process

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

Initial Touchpoint

A brief 15-to-20-minute phone screen or career fair interview discussing academic interests, software experience, and career goals.

What to demonstrate

  • A brief 15-to-20-minute phone screen or career fair interview discussing academic interests, software experience, and career goals
  • Depth in Object-Oriented Programming (OOP)

How to prepare

  • Answer aloud and timed: Walk me through a significant software project you worked on recently. What was your specific contribution, and what technical challenges did you overcome?
  • Answer aloud and timed: What are your primary academic and software engineering interests, and how do they align with our defense-focused research?

Onsite Interview

A comprehensive onsite interview where candidates deliver a 20-minute presentation on personal projects or past work.

What to demonstrate

  • A comprehensive onsite interview where candidates deliver a 20-minute presentation on personal projects or past work
  • Depth in Object-Oriented Programming (OOP)

How to prepare

  • Answer aloud and timed: Describe a time you had to work with a poorly specified requirement. How did you clarify the goals and deliver the solution?
  • Answer aloud and timed: How have you utilized version control and configuration management tools to collaborate on a multi-developer codebase?

Panel Discussion

Followed by one-on-one or small-group interviews with team members and the department head, blending discussions on the presentation and technical exercises.

What to demonstrate

  • Followed by one-on-one or small-group interviews with team members and the department head, blending discussions on the presentation and technical exercises
  • Depth in Object-Oriented Programming (OOP)

How to prepare

  • Answer aloud and timed: Write a basic algorithm (or pseudocode) on the whiteboard to solve a search or pathfinding problem on a coordinate grid.
  • Answer aloud and timed: Explain the key differences between memory management in C++ versus a garbage-collected language like Java or C#.

Where candidates lose points

Master Your Presentation

Treat your 20-minute presentation as the most important part of your preparation. Practice it multiple times to ensure it fits perfectly within the time limit, flows logically, and highlights your personal engineering contributions.

Clarify Vague Questions

Some whiteboard or technical discussion questions may be intentionally open-ended or poorly specified. Do not jump straight into writing code; ask clarifying questions first to define the scope, constraints, and requirements.

Emphasize Your Math Background

Toyon Research values strong mathematical skills. Be ready to talk about numerical methods, coordinate geometry, or optimization algorithms you have implemented, even if they were part of academic coursework.

Showcase Collaborative Tools

Highlight your experience with Git, version control, code reviews, and agile methodologies. The team highly values engineers who can seamlessly integrate into their collaborative development workflows.

Questions & practice

Write a basic algorithm (or pseudocode) on the whiteboard to solve a search or pathfinding problem on a coordi

Medium · Technical & Coding

Write a basic algorithm (or pseudocode) on the whiteboard to solve a search or pathfinding problem on a coordinate grid.

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?

Explain the key differences between memory management in C++ versus a garbage-collected language like Java or

Medium · Technical & Coding

Explain the key differences between memory management in C++ versus a garbage-collected language like Java or C#.

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?

How would you approach designing a system that requires real-time geographic data processing using GIS tools?

Medium · Technical & Coding

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?

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?

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

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

Walk me through a significant software project you worked on recently. What was your specific contribution, an

Medium · Project & Experience Walkthroughs

Walk me through a significant software project you worked on recently. What was your specific contribution, and what technical challenges did you overcome?

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?

What are your primary academic and software engineering interests, and how do they align with our defense-focu

Medium · Project & Experience Walkthroughs

What are your primary academic and software engineering interests, and how do they align with our defense-focused research?

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 have you utilized version control and configuration management tools to collaborate on a multi-developer c

Medium · Project & Experience Walkthroughs

How have you utilized version control and configuration management tools to collaborate on a multi-developer codebase?

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?

Exports duplicate a row range about once a week

Hard · leases · clock skew · idempotency

Roughly once a week an export writes a file containing a duplicated range of rows. The affected job_run rows show attempt = 1, status = succeeded, one started_at, and a lease_owner naming a different host from the one whose logs show the job starting. Leases last 30 seconds and are heartbeated every 10 from inside the handler; lease_expires_at is computed on the worker and compared against the database's now(). Find the mechanism, and give a fix that holds even if you cannot fix the clocks.

Approach

  1. Start from the fact that eliminates the obvious answer. attempt = 1 means no retry was recorded, so this is not a re-run after failure; two workers ran the same row concurrently and the takeover path never touched the counter. lease_owner naming a host other than the one that started the job is the same statement from the other side.
  2. Enumerate the mechanisms that cause a premature takeover, then find the signal that separates them. Either the lease genuinely expired because the heartbeat did not fire, which is what happens when the heartbeat runs on the handler's own thread and the handler makes a long blocking call, or it only appeared expired because two clocks disagree, since lease_expires_at is written from the worker's clock and evaluated against the database's. The discriminator is the distribution: incidents clustered on the longest exports indict the heartbeat, incidents clustered on one host indict skew. Measure both, and measure each host's offset against the database directly.
  3. Read the reclaim query precisely. In PostgreSQL now() is transaction start time, not statement time, so a reclaimer holding a long transaction compares against an older timestamp than expected; clock_timestamp() is the statement-time function. This is worth ruling in or out before you redesign anything, because it changes which rows look expired.
  4. Remove the second clock rather than trying to synchronise it. Issue and extend the lease in the database, with lease_expires_at = now() + interval '30 seconds' in both the claim and the heartbeat, so exactly one clock is ever compared and worker skew stops mattering to this predicate.

Follow-up

  • The displaced worker has already streamed half the file to object storage. What makes that side effect safe to repeat?
  • You now count takeovers. What alert fires on that counter, and at what threshold?

Suggested practice checklist

Built from the rounds and topics Toyon Research candidates report.

Day 1 — Map the Toyon Research loop

  • Write out the reported sequence: Initial Touchpoint, Onsite Interview, Panel Discussion.
  • 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 Object-Oriented Programming (OOP)

  • Spend the session on Object-Oriented Programming (OOP), which Toyon Research candidates report being tested on.
  • Write one worked example in Object-Oriented Programming (OOP) and time yourself on it.

Deliverable: One timed worked example in Object-Oriented Programming (OOP).

Day 3 — Work C++

  • Spend the session on C++, which Toyon Research candidates report being tested on.
  • Write one worked example in C++ and time yourself on it.

Deliverable: One timed worked example in C++.

Day 4 — Work GIS (Geographic Information Systems)

  • Spend the session on GIS (Geographic Information Systems), which Toyon Research candidates report being tested on.
  • Write one worked example in GIS (Geographic Information Systems) and time yourself on it.

Deliverable: One timed worked example in GIS (Geographic Information Systems).

Day 5 — Answer out loud: Project & Experience Walkthroughs

  • Answer aloud, timed: Walk me through a significant software project you worked on recently. What was your specific contribution, and what technical challenges did you overcome?
  • Answer aloud, timed: What are your primary academic and software engineering interests, and how do they align with our defense-focused research?

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

Day 6 — Answer out loud: Technical & Coding

  • Answer aloud, timed: Write a basic algorithm (or pseudocode) on the whiteboard to solve a search or pathfinding problem on a coordinate grid.
  • Answer aloud, timed: Explain the key differences between memory management in C++ versus a garbage-collected language like Java or C#.

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

Day 7 — Answer out loud: Behavioral & Collaboration

  • Answer aloud, timed: How do you handle constructive criticism or conflicting technical opinions during a code review?
  • Answer aloud, timed: Describe a situation where you had to explain a complex technical concept to a non-technical stakeholder or team member.

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

Behavioural preparation

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

Describe a time you had to work with a poorly specified requirement. How did you clarify the goals and deliver

Medium · Project & Experience Walkthroughs

Describe a time you had to work with a poorly specified requirement. How did you clarify the goals and deliver the solution?

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 your experience with coding and testing numerical methods or mathematical models.

Medium · Technical & Coding

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 constructive criticism or conflicting technical opinions during a code review?

Medium · Behavioral & Collaboration

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 explain a complex technical concept to a non-technical stakeholder or te

Medium · Behavioral & Collaboration

Describe a situation where you had to explain a complex technical concept to a non-technical stakeholder or team member.

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?

Why are you interested in working within the defense and aerospace industry, and what motivates you to support

Medium · Behavioral & Collaboration

Why are you interested in working within the defense and aerospace industry, and what motivates you to support government customers?

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?