# Software Engineer
**Role:** Software Engineer · **Level:** L2
**Company:** [Citadel](https://scaleengineer.com/companies/citadel)
**Difficulty:** Medium
**Salary:** US$110000 - US$140000
**Experience:** 2 - 5
**Timeline:** ~14 days
This interview process is for a Software Engineer (L2) position at Citadel. It is designed to assess a candidate's technical skills, problem-solving abilities, and cultural fit within the company.
Canonical: https://scaleengineer.com/interviews/citadel/l2-software-engineer
---
## Overall evaluation

- Technical Skills
- Problem-Solving
- Communication & Collaboration
- Cultural Fit

## Questions asked

- Write a function to find the kth smallest element in a sorted matrix.
- Design a rate limiter for an API.
- Tell me about a time you had to deal with a production issue.
- What are the differences between TCP and UDP?
- How would you optimize a slow database query?
- Describe your experience with cloud platforms (AWS, Azure, GCP).
- What is object-oriented programming and its principles?
- Explain the concept of recursion with an example.
- How do you ensure code quality in a team project?
- What are your strengths and weaknesses as a software engineer?

## Preparation tips

### lists

- Review fundamental computer science concepts, including data structures, algorithms, and operating systems.
- Practice coding problems on platforms like LeetCode, HackerRank, or AlgoExpert, focusing on medium-difficulty problems.
- Study system design principles and common architectural patterns.
- Prepare to discuss your past projects and technical experiences in detail.
- Research Citadel's business, culture, and recent news.
- Prepare thoughtful questions to ask the interviewer.
- Practice behavioral questions using the STAR method (Situation, Task, Action, Result).

### studyPlan

- {"title":"Data Structures and Algorithms","longDescription":"Weeks 1-2: Focus on Data Structures (Arrays, Linked Lists, Stacks, Queues, Trees, Graphs, Hash Tables) and their common algorithms (Sorting, Searching, Graph Traversal). Practice implementing these from scratch 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. Cover topics like scalability, availability, reliability, databases (SQL vs. NoSQL), caching, load balancing, and microservices. Study common design patterns and practice designing systems like Twitter feed or URL shortener.","shortDescription":"Weeks 3-4: System Design principles. Study scalability, databases, caching, and practice design problems."}
- {"title":"Behavioral and Situational Preparation","longDescription":"Week 5: Prepare for Behavioral and Situational questions. Reflect on your past experiences and prepare examples using the STAR method. Understand Citadel's values and how your experiences align with them.","shortDescription":"Week 5: Behavioral & Situational questions. Prepare STAR method examples and research company values."}
- {"title":"Final Preparation and Mock Interviews","longDescription":"Week 6: Mock interviews and final review. Conduct mock interviews to simulate the actual interview environment. Review all topics, focusing on areas where you feel less confident. Prepare questions for the interviewer.","shortDescription":"Week 6: Mock interviews and final review. Practice coding, system design, and behavioral questions."}

## Location differences

- {"location":"New York","differences":{"tips":["Be prepared to discuss specific examples from your experience.","Emphasize your thought process when solving problems.","Showcase your ability to work effectively in a team."],"interviewFocus":["Problem-solving methodologies","Code quality and best practices","Collaboration and communication"],"commonQuestions":["Discuss a challenging technical problem you solved in your previous role.","How do you approach debugging complex issues?","Describe a time you had to work with a difficult stakeholder."]}}
- {"location":"Chicago","differences":{"tips":["Brush up on common algorithms and data structures.","Practice system design case studies.","Be ready to articulate your reasoning clearly."],"interviewFocus":["Data structures and algorithms","System design principles","Technical decision-making"],"commonQuestions":["Explain the trade-offs between different data structures for a given problem.","How would you design a system to handle a large volume of requests?","Tell me about a time you disagreed with a technical decision and how you handled it."]}}

## Round 1: Coding Challenge
**Type:** Technical Interview - Data Structures and Algorithms · **Difficulty:** Medium · **Duration:** 45 min
Assess core coding skills through problem-solving.
This round focuses on your core technical skills, primarily data structures and algorithms. You will be asked to solve one or two coding problems on a whiteboard or shared coding environment. The interviewer will assess your ability to understand the problem, devise an efficient solution, implement it correctly, and explain your reasoning. Be prepared to discuss time and space complexity.
**Interviewers look for:** Strong understanding of data structures and algorithms.; Ability to write clean, efficient, and well-structured code.; Logical thinking and systematic problem-solving.; Communication of thought process.
**Evaluation criteria:** Correctness of the solution.; Efficiency of the algorithm (time and space complexity).; Code clarity and readability.; Ability to handle edge cases.; Problem-solving approach.
**Common rejection reasons:** Inability to articulate thought process clearly.; Lack of fundamental data structures and algorithms knowledge.; Poor coding style or inefficient solutions.; Failure to consider edge cases.
## Questions

- Given an array of integers, find the contiguous subarray with the largest sum.
- Implement a function to reverse a linked list.
- Find the lowest common ancestor of two nodes in a binary tree.

## Preparation tips

- Practice coding problems on platforms like LeetCode, focusing on medium difficulty.
- Understand the time and space complexity of your solutions.
- Practice explaining your thought process out loud.
- Be comfortable with common data structures (arrays, linked lists, trees, graphs, hash maps) and algorithms (sorting, searching, dynamic programming).

## Round 2: System Design
**Type:** Technical Interview - System Design · **Difficulty:** Medium to Hard · **Duration:** 60 min
Assess ability to design scalable and robust software systems.
This round evaluates your ability to design and architect software systems. You'll be presented with a high-level problem (e.g., design Twitter's news feed, design a URL shortener) and expected to discuss various aspects of the system, including data models, APIs, scalability, and potential bottlenecks. Focus on clarifying requirements, making reasonable assumptions, and justifying your design choices.
**Interviewers look for:** Ability to design scalable and maintainable systems.; Knowledge of distributed systems concepts.; Pragmatic approach to problem-solving.; Ability to articulate design decisions and trade-offs.
**Evaluation criteria:** Understanding of scalability, availability, and reliability.; Ability to design robust and efficient systems.; Knowledge of various system components (databases, caches, load balancers).; Trade-off analysis and justification of design choices.; Clarity of communication.
**Common rejection reasons:** Lack of understanding of system design principles.; Inability to handle scale and performance considerations.; Poor trade-off analysis.; Difficulty in communicating design choices.
## Questions

- Design a system like TinyURL.
- Design a distributed cache.
- How would you design a notification service?

## Preparation tips

- Study common system design concepts (load balancing, caching, databases, message queues).
- Practice designing well-known systems.
- Be prepared to discuss trade-offs between different approaches.
- Understand how to scale systems to handle large amounts of traffic and data.

## Round 3: Managerial Round
**Type:** Behavioral Interview · **Difficulty:** Medium · **Duration:** 45 min
Assess behavioral competencies and cultural fit.
This round is typically with the hiring manager and focuses on your behavioral and situational questions. The goal is to understand your past experiences, how you handle challenges, your teamwork abilities, and your overall fit with the team and company culture. Use the STAR method to structure your answers and provide concrete examples.
**Interviewers look for:** Cultural fit.; Motivation and passion for software engineering.; Ability to work effectively in a team.; Self-awareness and ability to learn from experiences.
**Evaluation criteria:** Teamwork and collaboration skills.; Problem-solving approach and adaptability.; Communication clarity.; Alignment with company values.; Motivation and career aspirations.
**Common rejection reasons:** Poor communication skills.; Lack of enthusiasm or interest.; Inability to provide specific examples for behavioral questions.; Mismatch with team culture or company values.
## Questions

- Tell me about a time you faced a significant challenge at work and how you overcame it.
- Describe a situation where you had to work with a difficult team member.
- Why are you interested in working at Citadel?

## Preparation tips

- Prepare examples for common behavioral questions (teamwork, conflict resolution, leadership, failure).
- Use the STAR method (Situation, Task, Action, Result) to structure your answers.
- Research Citadel's values and culture.
- Be ready to discuss your career goals and why you are interested in this role.