# Software Engineer
**Role:** Software Engineer · **Level:** L3
**Company:** [Citadel](https://scaleengineer.com/companies/citadel)
**Difficulty:** Medium
**Salary:** US$90000 - US$120000
**Experience:** 1 - 3
**Timeline:** ~14 days
This interview process is for a Software Engineer position at Citadel, specifically for the L3 level. 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/l3-software-engineer
---
## Overall evaluation

- Technical Skills
- System Design & Architecture
- Behavioral & Cultural Fit

## Questions asked

- Write a function to reverse a linked list.
- Given an array of integers, find the two numbers that add up to a specific target.
- Design a system to handle real-time notifications.
- Tell me about a time you faced a technical challenge and how you overcame it.
- How would you optimize a slow database query?

## Preparation tips

### lists

- Review fundamental computer science concepts.
- Practice coding problems regularly, focusing on time and space complexity.
- Prepare for behavioral questions by thinking about your past experiences using the STAR method (Situation, Task, Action, Result).
- Research Citadel's values, mission, and recent projects.
- Prepare thoughtful questions to ask the interviewer.

### studyPlan

- {"title":"Data Structures and Algorithms Fundamentals","longDescription":"Weeks 1-2: Focus on core data structures (arrays, linked lists, stacks, queues, trees, hash maps) and their time/space complexity. Practice basic algorithms like sorting (merge sort, quicksort) and searching (binary search).","shortDescription":"Weeks 1-2: Data Structures & Basic Algorithms. Cover arrays, linked lists, trees, sorting, searching."}
- {"title":"Algorithm Design and Analysis","longDescription":"Weeks 3-4: Dive deeper into algorithms, including dynamic programming, graph traversal (BFS, DFS), and greedy algorithms. Practice medium-difficulty coding problems on platforms like LeetCode.","shortDescription":"Weeks 3-4: Advanced Algorithms & Problem Solving. Focus on DP, graphs, greedy algorithms. Practice medium LeetCode problems."}
- {"title":"System Design Introduction","longDescription":"Week 5: Begin studying system design concepts. Understand topics like API design, database choices (SQL vs. NoSQL), caching strategies, load balancing, and microservices architecture. Review common system design interview questions.","shortDescription":"Week 5: System Design Basics. Cover APIs, databases, caching, load balancing."}
- {"title":"System Design and Behavioral Preparation","longDescription":"Week 6: Continue with system design, focusing on scalability, reliability, and distributed systems. Practice designing common systems like a URL shortener or a Twitter feed. Also, prepare for behavioral questions.","shortDescription":"Week 6: Advanced System Design & Behavioral Prep. Practice designing systems, prepare STAR method answers."}

## Location differences

- {"location":"New York","differences":{"tips":["Research common business practices in this region.","Be prepared to discuss your experience with local technologies or frameworks.","Understand the company's presence and impact in this specific location."],"interviewFocus":["Adaptability to local work culture","Communication skills in the local language (if applicable)","Understanding of local market trends"],"commonQuestions":["Tell me about a challenging project you worked on.","How do you handle tight deadlines?","Describe a time you disagreed with a teammate."]}}
- {"location":"London","differences":{"tips":["Brush up on fundamental data structures (arrays, linked lists, trees, graphs) and algorithms (sorting, searching, dynamic programming).","Practice coding problems on platforms like LeetCode or HackerRank.","Be ready to explain your thought process clearly and concisely."],"interviewFocus":["Core computer science fundamentals","Proficiency in data structures and algorithms","Problem-solving approach"],"commonQuestions":["How do you approach debugging complex issues?","Can you explain the concept of Big O notation?","Describe your experience with version control systems like Git."]}}
- {"location":"Chicago","differences":{"tips":["Review common system design patterns and trade-offs.","Be prepared to discuss trade-offs in different architectural choices.","Understand concepts like caching, load balancing, and database scaling."],"interviewFocus":["System design and architecture","Scalability and performance optimization","Experience with distributed systems"],"commonQuestions":["Tell me about your experience with cloud platforms (AWS, Azure, GCP).","How do you ensure the scalability and reliability of your code?","Describe a situation where you had to optimize code for performance."]}}

## Round 1: Data Structures and Algorithms Round
**Type:** Technical Interview - Data Structures and Algorithms · **Difficulty:** Medium · **Duration:** 45 min
Coding challenge focused on data structures and algorithms.
This round focuses on your fundamental programming skills. You will be asked to solve coding problems that test your knowledge of data structures and algorithms. The interviewer will assess how you approach the problem, your ability to write clean and efficient code, and how you handle edge cases. Expect to write code on a whiteboard or a shared online editor.
**Interviewers look for:** Clear communication of thought process; Ability to break down complex problems; Proficiency in coding; Understanding of edge cases
**Evaluation criteria:** Correctness of the solution; Efficiency of the solution (time and space complexity); Code quality and readability; Problem-solving approach
**Common rejection reasons:** Inability to articulate thought process; Incorrect or inefficient algorithm; Code does not compile or has significant bugs
## Questions

- Given a binary tree, find its inorder traversal.
- Implement a function to find the kth smallest element in an unsorted array.

## Preparation tips

- Practice coding problems on platforms like LeetCode, HackerRank, or AlgoExpert.
- Understand the time and space complexity of your solutions.
- Be prepared to explain your code line by line.
- Practice explaining your thought process out loud.

## Round 2: System Design Round
**Type:** Technical Interview - System Design · **Difficulty:** Hard · **Duration:** 60 min
Design a scalable system to solve a given problem.
In this round, you will be presented with a high-level problem and asked to design a system to solve it. This could involve designing a social media feed, a URL shortener, or a distributed key-value store. The focus is on your ability to think about scalability, reliability, performance, and trade-offs in system design.
**Interviewers look for:** Ability to design complex systems; Knowledge of distributed systems concepts; Pragmatic approach to problem-solving; Consideration of various constraints
**Evaluation criteria:** Scalability of the proposed solution; Robustness and fault tolerance; Understanding of trade-offs; Clarity of design choices
**Common rejection reasons:** Lack of understanding of system design principles; Inability to handle scale or trade-offs; Poorly designed architecture
## Questions

- Design a system like Twitter's news feed.
- How would you design a rate limiter?

## Preparation tips

- Study common system design patterns and architectures.
- Read books like 'Designing Data-Intensive Applications'.
- Practice designing systems for common interview questions.
- Be prepared to discuss trade-offs between different technologies and approaches.

## Round 3: Behavioral and Managerial Round
**Type:** Behavioral Interview · **Difficulty:** Medium · **Duration:** 30 min
Assess your behavioral competencies and cultural fit.
This round is focused on understanding your past experiences, your motivations, and how you would fit into the team and company culture. You'll be asked behavioral questions about your strengths, weaknesses, how you handle conflict, and your career aspirations. Be prepared to provide specific examples using the STAR method.
**Interviewers look for:** How you handle challenges and conflicts; Your learning agility; Your passion for software engineering; Your alignment with Citadel's culture
**Evaluation criteria:** Communication skills; Teamwork and collaboration; Problem-solving approach; Motivation and alignment with company values
**Common rejection reasons:** Poor communication skills; Lack of enthusiasm or interest; Inability to provide specific examples; Poor cultural fit
## Questions

- Tell me about a time you failed and what you learned from it.
- How do you stay updated with new technologies?

## Preparation tips

- Prepare examples for common behavioral questions using the STAR method.
- Research Citadel's company culture and values.
- Be ready to discuss your career goals and why you are interested in this role.
- Ask thoughtful questions about the team and the company.