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Justpark Software Engineer Interview Guide

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

The 60-second brief

A Software Engineer at Justpark plays a critical role in scaling a high-transaction mobility platform that connects drivers with available parking spaces in real time. The engineering team is tasked with building and maintaining robust APIs, optimizing search and booking algorithms, and developing seamless user interfaces. Your work directly impacts millions of drivers and thousands of space owners, making the reliability, speed, and scalability of your code essential to the business's success. At Justpark, engineers do not work in isolation. You will collaborate closely with product managers, designers, and business operations teams to deliver feature-rich applications and hardware integrations, such as the Oobeo Platform.

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

Focus areas

  • Coding Challenges
  • Algorithms & Problem Solving
  • UI Development

The Justpark interview process

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

Phone Screen

Initial phone screen focused on your background, experience, and high-level fit for the role.

What to demonstrate

  • Initial phone screen focused on your background, experience, and high-level fit for the role
  • Depth in Coding Challenges

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

Includes a take-home coding challenge or a technical phone interview.

What to demonstrate

  • Includes a take-home coding challenge or a technical phone interview
  • Depth in Coding Challenges

How to prepare

  • Answer aloud and timed: How do you handle race conditions when two users attempt to book the same parking space simultaneously?
  • Answer aloud and timed: Describe how you would build and structure a RESTful API to expose parking space availability data to third-party partners.

Onsite Panel Loop

An intensive, multi-hour 'working day' where you interact with developers, product managers, and business leaders.

What to demonstrate

  • An intensive, multi-hour 'working day' where you interact with developers, product managers, and business leaders
  • Depth in Coding Challenges

How to prepare

  • Answer aloud and timed: How would you optimize a slow-running SQL query that retrieves location-based search results for a mobile client?
  • Answer aloud and timed: Implement an algorithm to find the closest available parking spot given a set of GPS coordinates.

Where candidates lose points

Test your take-home code thoroughly

Ensure that your coding submission runs cleanly without environment errors. If you are using a local SQLite database or specific dependencies, document the setup steps clearly in a README file.

Expect repetitive panel questions

Because you will meet with different teams (developers, PMs, and business leaders), you may find yourself answering similar questions about your background. Stay enthusiastic and keep your answers consistent and structured.

Understand the business model

Familiarize yourself with how Justpark operates, its value proposition for both drivers and space owners, and key product offerings like the Oobeo Platform. Showing domain interest goes a long way.

Be proactive with communication

If you encounter ambiguities in a prompt or face technical issues during a live coding session, speak your thoughts aloud. Interviewers want to see how you collaborate and solve problems in real time.

Questions & practice

Implement an algorithm to find the closest available parking spot given a set of GPS coordinates.

Medium · Coding & Algorithmic Problem Solving

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?

Write a function to merge overlapping time intervals representing reserved parking slots.

Medium · Coding & Algorithmic Problem Solving

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?

Build a lightweight UI component that dynamically filters and displays a list of search results based on user

Medium · Coding & Algorithmic Problem Solving

Build a lightweight UI component that dynamically filters and displays a list of search results based on user input.

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 slow-running SQL query that retrieves location-based search results for a mobile clie

Medium · Technical & System Design

How would you optimize a slow-running SQL query that retrieves location-based search results for a mobile client?

Approach

  1. Name the grain you start from and join outward from it.
  2. Check whether any join is one-to-many before aggregating, or the sums inflate.
  3. Say which index the query would use, and what makes it unusable.
  4. Handle the rows that do not match: that is usually the actual question.

Follow-up

  • How does the query change if that join becomes one-to-many?
  • What happens to this when the table is ten times larger?

Stop tag and share joins from fanning out a page

Medium · join fan-out · semi-joins · many-to-many

resource_tag is (resource_id, tag_id) with PK (resource_id, tag_id); resource_share is (resource_id, shared_with_user_id, permission). The tagged-and-shared listing inner-joins resource to both, filters tenant_id, tag_id = ANY($2) and shared_with_user_id = $3, orders by updated_at DESC and takes 50. Pages come back with fewer than 50 distinct resources and the total in the header is far too high. Explain the row multiplication, rewrite both the page query and the count query so each is correct, and name the index each one needs. PostgreSQL 16.

Approach

  1. Do the arithmetic against the predicates that are actually there. An inner join emits one row per matching child row, and both joins are filtered: tag_id = ANY($2) admits only the requested tags, shared_with_user_id = $3 admits one user's share rows. So a resource holding three of the requested tags and shared with $3 once yields three rows, not one — the multiplier is its count of matching tags times its share rows for that single user, and that second factor is 1 unless the table admits duplicate (resource_id, shared_with_user_id) pairs. LIMIT 50 then limits rows rather than resources, and COUNT(*) counts pairs — the header is the product, not the population.
  2. Reject DISTINCT as the fix. It deduplicates after the product has been built, so the planner must materialise and sort the fanned-out set before the LIMIT can apply, and it leaves any SUM or AVG in the same select list wrong.
  3. Rewrite both filters as semi-joins, keeping resource as the only row source: AND EXISTS (SELECT 1 FROM resource_tag rt WHERE rt.resource_id = r.resource_id AND rt.tag_id = ANY($2)) and the same shape against resource_share. A semi-join stops at the first match per resource and preserves the driving index order, so ORDER BY updated_at DESC, resource_id DESC LIMIT 50 still stops after 50 rows.
  4. Count with the same predicates and no join at all: SELECT count(*) FROM resource r WHERE r.tenant_id = $1 AND r.status = 'active' AND EXISTS (...) AND EXISTS (...). Nothing multiplies a resource, so the number is the population.

Follow-up

  • The filter changes from 'any of these tags' to 'all of these tags'. Rewrite it and state what it costs relative to the ANY form.
  • A resource can be shared with the same user twice under different permissions. Does your count change, and should it?

How would you design a database schema to support a real-time parking spot reservation system?

Medium · Technical & System Design

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 are the trade-offs of using an embedded database like SQLite versus a fully managed relational database i

Medium · Technical & System Design

What are the trade-offs of using an embedded database like SQLite versus a fully managed relational database in production?

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?

Describe how you would build and structure a RESTful API to expose parking space availability data to third-pa

Medium · Technical & System Design

Describe how you would build and structure a RESTful API to expose parking space availability data to third-party partners.

Approach

  1. Say who the caller is and what they do when the call fails halfway.
  2. Define the identity of a request so a retry cannot double-apply it.
  3. Separate accepted, pending, failed and confirmed; they are different facts.
  4. Design the error taxonomy before the success shape; callers branch on it.

Follow-up

  • What happens if the caller retries after a timeout?
  • How does a client discover it is on an old version of this contract?

How would you implement a rate-limiter for an API endpoint to prevent abuse?

Medium · Coding & Algorithmic Problem Solving

Approach

  1. Say who the caller is and what they do when the call fails halfway.
  2. Define the identity of a request so a retry cannot double-apply it.
  3. Separate accepted, pending, failed and confirmed; they are different facts.
  4. Design the error taxonomy before the success shape; callers branch on it.

Follow-up

  • What happens if the caller retries after a timeout?
  • How does a client discover it is on an old version of this contract?

Debug a provided codebase containing hidden database connection and state-handling errors.

Medium · Coding & Algorithmic Problem Solving

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 Justpark candidates report.

Day 1 — Map the Justpark loop

  • Write out the reported sequence: Phone Screen, Technical Evaluation, Onsite Panel Loop.
  • 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 Coding Challenges

  • Spend the session on Coding Challenges, which Justpark candidates report being tested on.
  • Write one worked example in Coding Challenges and time yourself on it.

Deliverable: One timed worked example in Coding Challenges.

Day 3 — Work Algorithms & Problem Solving

  • Spend the session on Algorithms & Problem Solving, which Justpark candidates report being tested on.
  • Write one worked example in Algorithms & Problem Solving and time yourself on it.

Deliverable: One timed worked example in Algorithms & Problem Solving.

Day 4 — Work UI Development

  • Spend the session on UI Development, which Justpark candidates report being tested on.
  • Write one worked example in UI Development and time yourself on it.

Deliverable: One timed worked example in UI Development.

Day 5 — Answer out loud: Technical & System Design

  • Answer aloud, timed: How would you design a database schema to support a real-time parking spot reservation system?
  • Answer aloud, timed: What are the trade-offs of using an embedded database like SQLite versus a fully managed relational database in production?

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

Day 6 — Answer out loud: Coding & Algorithmic Problem Solving

  • Answer aloud, timed: Implement an algorithm to find the closest available parking spot given a set of GPS coordinates.
  • Answer aloud, timed: Write a function to merge overlapping time intervals representing reserved parking slots.

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

Day 7 — Answer out loud: Behavioral & Alignment

  • Answer aloud, timed: Describe a time when you had to deliver a feature under a tight deadline with incomplete requirements. How did you prioritize?
  • Answer aloud, timed: How do you handle technical disagreements with other developers or product managers?

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

Behavioural preparation

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

How do you handle race conditions when two users attempt to book the same parking space simultaneously?

Medium · Technical & System Design

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 time when you had to deliver a feature under a tight deadline with incomplete requirements. How did

Medium · Behavioral & Alignment

Describe a time when you had to deliver a feature under a tight deadline with incomplete requirements. How did you prioritize?

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 technical disagreements with other developers or product managers?

Medium · Behavioral & Alignment

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?

Tell me about a complex technical bug you encountered in production and the steps you took to diagnose and res

Medium · Behavioral & Alignment

Tell me about a complex technical bug you encountered in production and the steps you took to diagnose and resolve it.

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 do you want to work at Justpark, and how does your past experience align with our mission to simplify park

Medium · Behavioral & Alignment

Why do you want to work at Justpark, and how does your past experience align with our mission to simplify parking?

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 learn a new technology or framework quickly to solve a business problem.

Medium · Behavioral & Alignment

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?