# Software Engineer 1
**Role:** Software Engineer · **Level:** L4
**Company:** [Affirm](https://scaleengineer.com/companies/affirm)
**Difficulty:** Medium
**Salary:** US$110000 - US$140000
**Experience:** 2 - 5
**Timeline:** ~10 days
The Software Engineer 1 (L4) interview at Affirm is designed to assess a candidate's foundational software engineering skills, problem-solving abilities, and cultural fit. It typically involves a mix of technical and behavioral assessments to ensure the candidate can contribute effectively to Affirm's engineering teams.
Canonical: https://scaleengineer.com/interviews/affirm/l4-software-engineer
---
## Overall evaluation

- Technical Skills
- Communication
- Collaboration & Teamwork
- Cultural Fit

## Questions asked

- Write a function to reverse a linked list.
- Given an array of integers, find the contiguous subarray with the largest sum.
- Design a system to store and retrieve user profiles.
- Explain the concept of RESTful APIs.
- Tell me about a time you failed and what you learned from it.
- How would you optimize a slow database query?
- Describe your experience with version control systems like Git.

## Preparation tips

### lists

- Review fundamental data structures (arrays, linked lists, trees, graphs, hash maps) and algorithms (sorting, searching, dynamic programming, graph traversal).
- Practice coding problems on platforms like LeetCode, HackerRank, or Coderbyte, focusing on medium-difficulty problems.
- Brush up on core computer science concepts such as operating systems, databases, and networking.
- Prepare for behavioral questions using the STAR method (Situation, Task, Action, Result).
- Understand Affirm's business, products, and engineering culture.
- Prepare questions to ask the interviewer about the role, team, and company.

### studyPlan

- {"title":"Data Structures & Complexity","longDescription":"Weeks 1-2: Focus on Data Structures. Cover arrays, linked lists, stacks, queues, hash tables, trees (binary trees, BSTs, heaps), and graphs. Practice implementing these and solving problems related to them. Understand time and space complexity (Big O notation).","shortDescription":"Weeks 1-2: Data Structures (Arrays, Lists, Trees, Graphs, Hash Tables) & Complexity Analysis."}
- {"title":"Algorithms & Problem Solving","longDescription":"Weeks 3-4: Focus on Algorithms. Cover sorting algorithms (quicksort, mergesort), searching algorithms (binary search), recursion, dynamic programming, greedy algorithms, and graph algorithms (BFS, DFS, Dijkstra's). Practice solving problems using these algorithms.","shortDescription":"Weeks 3-4: Algorithms (Sorting, Searching, DP, Graphs) & Problem Solving."}
- {"title":"System Design Fundamentals","longDescription":"Week 5: System Design Fundamentals. Understand concepts like scalability, availability, reliability, load balancing, caching, databases (SQL vs. NoSQL), and APIs. Practice designing common systems like a URL shortener or a Twitter feed.","shortDescription":"Week 5: System Design Basics (Scalability, Databases, Caching, APIs)."}
- {"title":"Behavioral & Mock Interviews","longDescription":"Week 6: Behavioral Preparation & Mock Interviews. Prepare answers for common behavioral questions using the STAR method. Focus on demonstrating ownership, teamwork, and problem-solving. Conduct mock interviews to simulate the actual interview experience.","shortDescription":"Week 6: Behavioral Questions (STAR method) & Mock Interviews."}

## Location differences

- {"location":"San Francisco, USA","differences":{"tips":["Be prepared to whiteboard solutions for common data structures and algorithms problems.","Practice explaining your thought process clearly and concisely.","Research Affirm's products and values to tailor your behavioral answers."],"interviewFocus":["Emphasis on practical coding skills and understanding of core CS concepts.","Assessment of collaboration and communication skills in a team setting."],"commonQuestions":["How would you design a URL shortener?","Explain the difference between a process and a thread.","Describe a challenging technical problem you solved and how you approached it.","Tell me about a time you disagreed with a teammate and how you resolved it."]}}
- {"location":"Remote (Global)","differences":{"tips":["Prepare for system design questions, focusing on trade-offs and scalability.","Be ready to discuss your experience with distributed systems and cloud technologies.","Highlight instances where you've taken initiative and driven projects forward."],"interviewFocus":["Greater emphasis on system design and scalability for more experienced candidates.","Assessment of adaptability and problem-solving in complex scenarios."],"commonQuestions":["How would you design a system to handle real-time notifications?","Discuss the trade-offs between SQL and NoSQL databases.","Describe a project where you had to optimize performance. What techniques did you use?","How do you handle ambiguity in project requirements?"]}}

## Round 1: Data Structures & Algorithms
**Type:** Technical (Coding) · **Difficulty:** Medium · **Duration:** 45 min
Coding challenge focused on data structures and algorithms.
This round typically involves a coding challenge, often presented as a problem to solve on a shared editor or whiteboard. The interviewer will assess your ability to translate a problem into code, your understanding of data structures and algorithms, and your approach to testing and debugging. Expect to discuss your solution and its time/space complexity.
**Interviewers look for:** A structured approach to problem-solving; Clean, efficient, and correct code; Ability to explain the solution and its trade-offs; Basic understanding of CS fundamentals
**Evaluation criteria:** Problem-solving approach; Coding proficiency; Understanding of data structures and algorithms; Communication clarity
**Common rejection reasons:** Inability to articulate thought process; Poor coding practices (unreadable, inefficient code); Fundamental misunderstanding of data structures or algorithms; Lack of enthusiasm or engagement
## Questions

- Given a string, find the length of the longest substring without repeating characters.
- Implement a function to check if a binary tree is a Binary Search Tree (BST).

## Preparation tips

- Practice coding problems under timed conditions.
- Focus on writing clean, readable, and well-commented code.
- Be prepared to explain your code line by line.
- Think about edge cases and how to handle them.

## Round 2: System Design & Architecture
**Type:** Technical (System Design) · **Difficulty:** Medium · **Duration:** 45 min
System design problem to assess architectural thinking.
This round assesses your ability to design scalable, reliable, and maintainable software systems. You'll be given an open-ended problem (e.g., design a social media feed, a URL shortener, or a rate limiter) and expected to discuss various components, data models, APIs, and trade-offs. The focus is on your thought process and ability to handle complexity.
**Interviewers look for:** A systematic approach to designing complex systems; Understanding of distributed systems concepts; Ability to identify and mitigate potential bottlenecks; Clear communication of design decisions and justifications
**Evaluation criteria:** System design principles; Scalability and performance considerations; Trade-off analysis; Clarity of design explanation; Handling of constraints and requirements
**Common rejection reasons:** Inability to design scalable and reliable systems; Lack of consideration for trade-offs; Poor communication of design choices; Not addressing potential failure points
## Questions

- Design a system like TinyURL.
- Design a news feed system for a social media platform.

## Preparation tips

- Study common system design patterns and architectures.
- Practice designing various types of systems.
- Focus on understanding trade-offs between different design choices.
- Be prepared to discuss databases, caching, load balancing, and message queues.

## Round 3: Behavioral Interview
**Type:** Behavioral & Cultural Fit · **Difficulty:** Medium · **Duration:** 45 min
Behavioral questions to assess fit and past experiences.
This round focuses on your past experiences and how they align with the role and Affirm's culture. You'll be asked behavioral questions designed to understand your work style, how you handle challenges, collaborate with others, and demonstrate key competencies. Use the STAR method to provide structured and specific answers.
**Interviewers look for:** Evidence of past behavior that predicts future performance; Alignment with Affirm's core values; Ability to collaborate effectively; Self-awareness and a growth mindset
**Evaluation criteria:** Behavioral competencies (teamwork, problem-solving, initiative); Cultural fit with Affirm's values; Communication and interpersonal skills; Motivation and career aspirations
**Common rejection reasons:** Lack of alignment with company values; Poor communication or interpersonal skills; Inability to provide specific examples for behavioral questions; Negative attitude or lack of enthusiasm
## Questions

- Tell me about a time you had to work with a difficult colleague. How did you handle it?
- Describe a project where you took initiative beyond your defined responsibilities.
- What are your career goals for the next 3-5 years?

## Preparation tips

- Prepare stories for common behavioral questions (teamwork, conflict resolution, failure, success, leadership).
- Be honest and authentic in your responses.
- Connect your experiences to Affirm's values.
- Show enthusiasm for the role and the company.