o9 Solutions Software Engineer interview questions & guide 2026

The questions below are representative of the patterns identified in recent interview experiences. While exact questions vary by team and interviewer, you should prepare for a rigorous assessment of your technical fundamentals and your ability to articulate your past work.

Technical Fundamentals & Coding

These questions assess your grasp of data structures, algorithms, and the ability to write optimized, clean code under pressure.

• Find the second highest number in an array without using built-in libraries.
• Implement a stack using two queues.

Preparation at o9 Solutions requires a balance of theoretical knowledge and practical, hands-on experience. The interviewers are looking for engineers who do not just "know" the concepts but can apply them to solve complex, real-world business challenges.

Role-related Knowledge – You must have a deep, granular understanding of the languages and tools listed on your resume. Expect to explain the "why" behind your technical decisions, such as why a specific database schema or microservices pattern was chosen.

Problem-solving Ability – Beyond writing code, you will be evaluated on how you structure your thoughts during a whiteboard or coding session. Focus on optimization, edge-case consideration, and the ability to articulate your logic as you work.

Technical Communication – You will often be asked to explain your projects or concepts to architects or senior engineers. Clarity, precision, and the ability to handle critical, probing follow-up questions are essential markers of a strong candidate.

Resilience & Professionalism – Some interviewers may challenge your answers or adopt a high-pressure demeanor to test your composure. Remain professional, objective, and focused on the technical problem at hand, regardless of the interviewer's tone.

The interview process at o9 Solutions is structured to be thorough, often spanning multiple rounds that progress from technical screening to deep-dive architecture and behavioral assessments. You should expect a pace that is both rapid and rigorous, with a strong emphasis on your technical depth and alignment with the team's ongoing projects.

The process typically begins with an online assessment or coding challenge, followed by a series of technical interviews with engineers and architects. These rounds are designed to scrutinize your past work and your fundamental computer science knowledge. You may also encounter behavioral rounds or discussions with hiring managers, where the focus shifts toward your experience, career goals, and how you handle complex professional environments.

The timeline above reflects the typical progression from initial screening to final technical and behavioral evaluations. Use this to pace your study—prioritize coding and SQL fundamentals early, and save your "project defense" preparation for the later, more conversational rounds.

Data Structures & Algorithms

This is the bedrock of the technical evaluation. You are expected to know how to implement and optimize standard data structures.

• Core focus: Arrays, Hashmaps, Stacks, Queues, and Trees.
• Advanced concepts: Balancing binary search trees, heap operations, and Big O notation for complex algorithms.
• Example scenarios: "Implement a data structure with specific operations in minimum time complexity" or "Optimize an existing algorithm provided in a half-implemented state."

As a Software Engineer at o9 Solutions, your work centers on the development and maintenance of complex planning software. You will be expected to collaborate closely with product managers and other engineers to translate business requirements into efficient, scalable code.

A primary responsibility is the ownership of your code—from design to deployment. You will frequently work with legacy systems, requiring the ability to read, understand, and modernize existing codebases without disrupting production environments. Additionally, you will participate in code reviews, architectural discussions, and cross-functional meetings, ensuring that the software you build meets the high performance and reliability standards required by the company's global client base.

A strong candidate for Software Engineer demonstrates a mix of strong computer science fundamentals and a pragmatic, problem-solving mindset.

• Must-have skills:
  • Proficiency in Python or C#.
  • Solid command of SQL (joins, subqueries, optimization).
  • Strong grasp of Data Structures and Algorithms (DSA).
  • Ability to explain and defend past projects in depth.
• Nice-to-have skills:
  • Experience with React or Node.js.
  • Familiarity with Docker, Git, and Linux environments.
  • Knowledge of Microservices architecture and DDD (Domain-Driven Design).
• Soft skills:
  • Ability to maintain composure under critical questioning.
  • Clear, concise communication during technical deep dives.
  • A proactive attitude toward learning and adapting to new technologies.

Q: How long should I prepare for the interview? A: Given the depth of the technical questioning, we recommend at least 2–4 weeks of focused study, specifically targeting SQL, DSA, and a thorough review of your own projects.

Q: What is the most common reason for rejection? A: Aside from technical gaps, candidates are often rejected if they cannot articulate the "why" behind the technologies used in their resume or if they fail to remain professional when challenged by an interviewer.

Q: Is the interview process remote? A: Yes, most interview stages are conducted online, though you should be prepared for potential variations depending on your location and the specific team you are interviewing with.

Q: How should I handle an interviewer who is being critical or rude? A: Maintain your professionalism. The interviewers may be testing your ability to handle stress. Focus on the technical facts, remain calm, and do not take the interaction personally.

• Own your resume: Every line on your resume is fair game. If you mention a technology, be prepared for a deep dive into its internal workings.
• Practice your "Guesstimates": Don't worry about getting the exact number right; interviewers are looking for the logic and the assumptions you make during the process.
• Prepare for "Live" coding: Whether it's a whiteboard or a screen-sharing session, practice writing clean, readable code while explaining your thought process out loud.
• Be ready for legacy code: You may be asked to analyze or debug existing code. Practice reading code as much as you practice writing it.

The Software Engineer role at o9 Solutions is a high-impact position that demands both technical rigor and the professional maturity to navigate complex architectural and team environments. Success in this process is rarely about luck; it is about demonstrating a deep, defensible mastery of your technical stack and maintaining a calm, analytical approach to problem-solving.

Focus your preparation on the core themes outlined here: technical fundamentals, resume-based project defense, and system-level thinking. By consistently demonstrating your logic and staying grounded in your experience, you will position yourself as a strong, capable contributor. You can explore additional interview insights, practice questions, and preparation resources on Dataford to further refine your strategy.

The compensation data provided offers a range to help you benchmark expectations for this role. Use this to understand the market positioning of the position and to prepare for salary discussions, keeping in mind that total compensation often includes base pay, performance bonuses, and equity components.