# Software Engineer
**Role:** Software Engineer · **Level:** Software Engineer I
**Company:** [Duolingo](https://scaleengineer.com/companies/duolingo)
**Difficulty:** Medium
**Salary:** US$85000 - US$110000
**Experience:** 0 - 2
**Timeline:** ~7 days
This interview process is designed to assess candidates for a Software Engineer I position at Duolingo. It evaluates technical skills, problem-solving abilities, cultural fit, and potential for growth within the company.
Canonical: https://scaleengineer.com/interviews/duolingo/software-engineer-i-software-engineer
---
## Overall evaluation

- Technical Skills
- Cultural Fit & Behavioral
- Work Ethic & Ownership

## Questions asked

- Tell me about a challenging technical problem you faced and how you solved it.
- How would you design a system to recommend new lessons to users based on their learning progress?
- What are your favorite programming languages and why?
- Describe a time you disagreed with a teammate and how you resolved it.
- How do you stay up-to-date with new technologies and trends in software engineering?
- Write a function to reverse a linked list.
- Explain the concept of recursion with an example.
- What are the differences between a process and a thread?
- How would you approach debugging a performance issue in a web application?
- Why are you interested in working at Duolingo?

## Preparation tips

### lists

- Review fundamental data structures and algorithms.
- Practice coding problems on platforms like LeetCode or HackerRank.
- Understand object-oriented programming principles.
- Brush up on your knowledge of system design concepts.
- Prepare to discuss your past projects and experiences using the STAR method (Situation, Task, Action, Result).
- Research Duolingo's products, mission, and values.
- Prepare questions to ask the interviewer about the role, team, and company culture.

### studyPlan

- {"title":"Data Structures and Algorithms","longDescription":"Weeks 1-2: Focus on core data structures (arrays, linked lists, trees, graphs, hash maps) and algorithms (sorting, searching, dynamic programming, recursion). Practice implementing these in your preferred language and analyze their time and space complexity.","shortDescription":"Weeks 1-2: Data Structures & Algorithms fundamentals. Practice implementations and complexity analysis."}
- {"title":"System Design","longDescription":"Weeks 3-4: Dive into system design concepts. Study topics like scalability, load balancing, database design (SQL vs. NoSQL), caching, and API design. Consider how these apply to a product like Duolingo.","shortDescription":"Weeks 3-4: System Design basics. Focus on scalability, databases, caching, and APIs."}
- {"title":"Behavioral Preparation","longDescription":"Week 5: Prepare for behavioral questions. Think about your past experiences and how they demonstrate key competencies like problem-solving, teamwork, and leadership. Use the STAR method to structure your answers.","shortDescription":"Week 5: Behavioral questions preparation. Use STAR method for past experiences."}
- {"title":"Resume and Questions","longDescription":"Week 6: Review your resume and be ready to discuss any project or experience in detail. Also, prepare thoughtful questions to ask the interviewer about the role, team, and Duolingo's culture.","shortDescription":"Week 6: Resume review and question preparation for interviewers."}

## Location differences

- {"location":"Global","differences":{"tips":["Familiarize yourself with Duolingo's product and mission.","Be prepared to discuss your past projects and contributions in detail.","Practice explaining technical concepts clearly and concisely."],"interviewFocus":["Understanding of core software engineering principles.","Ability to write clean, maintainable, and efficient code.","Problem-solving and debugging skills.","Collaboration and communication skills."],"commonQuestions":["How would you approach building a feature to track user progress in a new language course?","Describe a time you had to debug a complex issue in a production environment.","What are your thoughts on code reviews and how do you provide constructive feedback?"]}}
- {"location":"Pittsburgh, USA","differences":{"tips":["Research the specific team you are interviewing for and their tech stack.","Prepare to discuss system design principles and trade-offs.","Highlight any experience with distributed systems or large-scale applications."],"interviewFocus":["Deeper understanding of system design and scalability.","Experience with specific technologies relevant to the team's stack (e.g., Python, React, Go).","Ability to handle ambiguity and make sound technical decisions."],"commonQuestions":["How would you optimize a database query for a large user base?","Discuss your experience with cloud platforms like AWS or GCP.","What are the trade-offs between different data structures for a specific problem?"]}}

## Round 1: Technical Phone Screen
**Type:** Technical Screen · **Difficulty:** Medium · **Duration:** 45 min
Coding challenge focusing on data structures and algorithms.
This initial technical screen focuses on your core programming skills and problem-solving abilities. You will be asked to solve one or two coding problems, typically involving data structures and algorithms. The interviewer will assess your approach to problem-solving, your ability to write working code, and your understanding of time and space complexity.
**Interviewers look for:** Clear thinking process; Ability to write clean and efficient code; Understanding of fundamental CS concepts
**Evaluation criteria:** Problem-solving skills; Coding proficiency; Understanding of data structures and algorithms
**Common rejection reasons:** Inability to articulate thought process; Poor problem-solving approach; Lack of fundamental programming knowledge
## Questions

- Given an array of integers, find the two numbers that add up to a specific target.
- Implement a function to check if a binary tree is a valid Binary Search Tree.

## Preparation tips

- Practice coding problems on a whiteboard or shared editor.
- Think out loud and explain your thought process.
- Ask clarifying questions if the problem is unclear.
- Test your code with edge cases.

## Round 2: System Design
**Type:** System Design Interview · **Difficulty:** Medium · **Duration:** 60 min
Design a scalable system relevant to Duolingo's product.
This round assesses your ability to design and scale software systems. You'll be presented with a high-level design problem (e.g., designing a URL shortener, a social media feed, or a feature for Duolingo). The interviewer will evaluate your understanding of distributed systems, databases, caching, and other relevant technologies, as well as your ability to make informed design decisions and discuss trade-offs.
**Interviewers look for:** Structured approach to design problems; Knowledge of common system design patterns; Ability to justify design choices
**Evaluation criteria:** System design capabilities; Understanding of scalability and performance; Ability to handle trade-offs
**Common rejection reasons:** Inability to design scalable solutions; Poor understanding of system components; Lack of consideration for trade-offs
## Questions

- Design a system to track user progress across multiple Duolingo courses.
- How would you design a real-time notification system for Duolingo?

## Preparation tips

- Study common system design patterns and architectures.
- Practice designing systems for scalability and reliability.
- Be prepared to discuss trade-offs between different approaches.
- Think about potential bottlenecks and how to address them.

## Round 3: Behavioral and Hiring Manager Interview
**Type:** Behavioral Interview · **Difficulty:** Medium · **Duration:** 45 min
Assess behavioral competencies and cultural fit.
This interview focuses on your behavioral and cultural fit. The hiring manager will ask questions about your past experiences, how you handle challenges, your teamwork abilities, and your motivations for joining Duolingo. Be prepared to share specific examples using the STAR method.
**Interviewers look for:** Enthusiasm for Duolingo's mission; Ability to work effectively in a team; Self-awareness and reflection; Alignment with Duolingo's values
**Evaluation criteria:** Communication skills; Teamwork and collaboration; Cultural fit; Motivation and passion
**Common rejection reasons:** Poor communication skills; Lack of alignment with company values; Inability to provide specific examples
## Questions

- Tell me about a time you had to work with a difficult colleague. How did you handle it?
- Why are you interested in Duolingo and this specific role?
- Describe a project you are particularly proud of and your contribution to it.

## Preparation tips

- Research Duolingo's mission, values, and culture.
- Prepare examples using the STAR method for common behavioral questions.
- Be ready to discuss your career goals and why Duolingo is a good fit.
- Show genuine enthusiasm for the company and the role.