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aPriori Software Engineer Interview Guide

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

The 60-second brief

As a Software Engineer at aPriori, you are at the intersection of high-end software development and complex manufacturing technology. aPriori provides a platform that helps manufacturers estimate the cost and manufacturability of parts early in the design process. Your work directly impacts how global companies bring products to market, making engineering efficiency and cost-transparency a reality. In this role, you will tackle unique challenges that blend traditional software engineering with domain-specific requirements like geometry processing, manufacturing simulation, and database architecture. Whether you are working on the core engine that calculates production costs or building the interfaces that engineers use to optimize their designs, your contributions are critical to the company’s mission of accelerating product innovation.

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

Focus areas

  • Data Structures & Algorithms (Graphs)
  • Polygon Geometry (2D Polygons)
  • Edge Case Handling

The aPriori interview process

aPriori candidates report 4 rounds over 3-5 weeks. The stages below are what candidates describe, not a published process.

Screening Call

Initial call to assess candidate's fit and discuss the role.

What to demonstrate

  • Initial call to assess candidate's fit and discuss the role
  • Depth in Data Structures & Algorithms (Graphs)

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 Evaluation

In-depth assessment of technical skills and problem-solving abilities.

What to demonstrate

  • In-depth assessment of technical skills and problem-solving abilities
  • Depth in Data Structures & Algorithms (Graphs)

How to prepare

  • Answer aloud and timed: How do you approach complex geometry problems in a CAD or simulation environment?
  • Answer aloud and timed: What is your experience with database structure and optimization?

Multiple Stakeholder Interviews

Interviews with various stakeholders including technical managers and department heads.

What to demonstrate

  • Interviews with various stakeholders including technical managers and department heads
  • Depth in Data Structures & Algorithms (Graphs)

How to prepare

  • Answer aloud and timed: How would you approach a 2d polygon or graph algorithm problem?
  • Answer aloud and timed: Can you review this provided code snippet and describe the output behavior if specific changes were made?

Final-Round Interviews

Concluding interviews to finalize candidate assessment before decision.

What to demonstrate

  • Concluding interviews to finalize candidate assessment before decision
  • Depth in Data Structures & Algorithms (Graphs)

How to prepare

  • Answer aloud and timed: Are you comfortable working through contrived edge cases in a coding project?
  • Answer aloud and timed: Walk me through your resume and your specific contributions to past projects.

Where candidates lose points

Communication is Key

When solving problems, think out loud. Your process is as important as the final answer to the interviewer.

Know Your CV

Be prepared to discuss every project on your resume in detail, including the challenges you faced and how you overcame them.

Ask Strategic Questions

Use your time at the end of the interview to ask about the company’s product roadmap or how the engineering team approaches technical debt.

Follow Up

If you do not hear back within the expected timeframe, send a polite follow-up email. It is professional to stay engaged with your recruiter.

Questions & practice

How would you approach a 2d polygon or graph algorithm problem?

Medium · Coding and 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?

Can you review this provided code snippet and describe the output behavior if specific changes were made?

Medium · Coding and 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?

Are you comfortable working through contrived edge cases in a coding project?

Medium · Coding and 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?

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

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

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?

How would you describe the cost-efficiency of different casting processes?

Medium · Technical and Domain Knowledge

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 approach complex geometry problems in a CAD or simulation environment?

Medium · Technical and Domain Knowledge

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?

Listing latency scales with page size, not with filters

Easy · n+1 · latency · query batching

The tenant listing endpoint reads resource filtered by tenant_id and status, ordered by updated_at DESC, and returns each row plus the owner's display name from app_user and the actor of that resource's latest resource_revision. p99 is 55 ms at 10 rows per page and 1.4 s at 200. Database telemetry shows 401 statements per request, each under 1 ms, and nothing in the slow-query log. Diagnose the cause and give the fix, stating the statement count per request and the p99 you expect afterwards.

Approach

  1. Read the counters before forming a theory. 401 statements for 200 rows is one driver query plus two per row, and sub-millisecond execution with an empty slow-query log rules out a bad plan. The time is round trips, which is why it is invisible in every per-query metric and scales with rows returned rather than with filter selectivity.
  2. Name the two per-row statements from their normalised text: a single-row app_user lookup by user_id, and a resource_revision lookup by resource_id ordered by version DESC LIMIT 1. Confirm by dropping those two response fields and watching the statement count fall to one. That locates the calls in the serialisation layer, not the repository.
  3. Check that the arithmetic accounts for the whole gap. Measure one round trip to the replica in isolation; 400 trips at roughly 3 ms of network plus 0.2 ms of execution is about 1.3 s on top of a 55 ms baseline, which matches. If the multiplication had fallen short, the N+1 would only be part of the story and you would keep looking.
  4. Batch both lookups. Collect owner_user_ids and resource_ids from the driver query, then issue WHERE tenant_id = $1 AND user_id = ANY($2) for the users, and PostgreSQL's SELECT DISTINCT ON (resource_id) ... WHERE resource_id = ANY($2) ORDER BY resource_id, version DESC for the latest revision, which the UNIQUE (resource_id, version) index serves directly. On an engine without DISTINCT ON, use a lateral join or a row_number window. Three statements per request at any page size.

Follow-up

  • The page size is capped at 200 today. What breaks first if it is raised to 2,000, and is it still this bug?
  • How do you stop the next N+1 from reaching production, given that no individual query is slow and the endpoint's tests pass?

Suggested practice checklist

Built from the rounds and topics aPriori candidates report.

Day 1 — Map the aPriori loop

  • Write out the reported sequence: Screening Call, Technical Evaluation, Multiple Stakeholder Interviews, Final-Round Interviews.
  • 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 4 reported rounds, with the weakest marked.

Day 2 — Work Data Structures & Algorithms (Graphs)

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

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

Day 3 — Work Polygon Geometry (2D Polygons)

  • Spend the session on Polygon Geometry (2D Polygons), which aPriori candidates report being tested on.
  • Write one worked example in Polygon Geometry (2D Polygons) and time yourself on it.

Deliverable: One timed worked example in Polygon Geometry (2D Polygons).

Day 4 — Work Edge Case Handling

  • Spend the session on Edge Case Handling, which aPriori candidates report being tested on.
  • Write one worked example in Edge Case Handling and time yourself on it.

Deliverable: One timed worked example in Edge Case Handling.

Day 5 — Answer out loud: Technical and Domain Knowledge

  • Answer aloud, timed: How would you describe the cost-efficiency of different casting processes?
  • Answer aloud, timed: Can you explain your experience with manufacturing processes?

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

Day 6 — Answer out loud: Coding and Algorithms

  • Answer aloud, timed: How would you approach a 2d polygon or graph algorithm problem?
  • Answer aloud, timed: Can you review this provided code snippet and describe the output behavior if specific changes were made?

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

Day 7 — Answer out loud: Behavioral and Role Fit

  • Answer aloud, timed: Walk me through your resume and your specific contributions to past projects.
  • Answer aloud, timed: If I called your last employer, what would they say your biggest weakness was?

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

Behavioural preparation

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

Can you explain your experience with manufacturing processes?

Medium · Technical and Domain Knowledge

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?

What is your experience with database structure and optimization?

Medium · Technical and Domain Knowledge

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?

Walk me through your resume and your specific contributions to past projects.

Medium · Behavioral and Role Fit

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 I called your last employer, what would they say your biggest weakness was?

Medium · Behavioral and Role Fit

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 balance professional engineering requirements with your interests outside of work?

Medium · Behavioral and Role Fit

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?