# Software Engineer
**Role:** Software Engineer · **Level:** E3
**Company:** [DoorDash](https://scaleengineer.com/companies/doordash)
**Difficulty:** Medium to Hard
**Salary:** US$110000 - US$150000
**Experience:** 2 - 5
**Timeline:** ~7 days
The DoorDash Software Engineer E3 interview process is designed to assess a candidate's technical skills, problem-solving abilities, and cultural fit for the company. It typically involves multiple rounds, including HR screening, technical interviews focusing on data structures and algorithms, system design, and behavioral questions. The goal is to identify candidates who can contribute effectively to DoorDash's engineering teams and uphold its values.
Canonical: https://scaleengineer.com/interviews/doordash/e3-software-engineer
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## Overall evaluation

- Technical Proficiency
- Communication
- Behavioral and Cultural Fit

## Questions asked

- Given an array of integers, find the contiguous subarray with the largest sum.
- Design a system to shorten URLs.
- Explain the difference between a process and a thread.
- Describe a time you disagreed with a teammate and how you resolved it.
- How would you optimize a slow-loading web page?
- Implement a function to reverse a linked list.
- What are the trade-offs between using a relational database and a NoSQL database?
- Tell me about a project you are particularly proud of.
- How do you handle ambiguity in requirements?
- Design a notification system for a large-scale application.

## 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 AlgoExpert, focusing on medium and hard difficulty.
- Study system design concepts, including scalability, availability, reliability, and common design patterns (e.g., load balancing, caching, message queues).
- Prepare for behavioral questions by reflecting on your past experiences using the STAR method (Situation, Task, Action, Result).
- Research DoorDash's mission, values, and recent news to understand the company's business and culture.
- Prepare thoughtful questions to ask the interviewers about the role, team, and company.

### studyPlan

- {"title":"Data Structures and Algorithms","longDescription":"Weeks 1-2: Focus on core data structures and algorithms. Cover arrays, linked lists, stacks, queues, trees (binary trees, BSTs, heaps), graphs, and hash tables. Practice common algorithms like sorting (quicksort, mergesort), searching (binary search), recursion, and dynamic programming. Aim to solve 2-3 problems per day.","shortDescription":"Weeks 1-2: Data Structures & Algorithms Fundamentals. Practice 2-3 problems daily."}
- {"title":"System Design","longDescription":"Weeks 3-4: Dive into system design. Study concepts like API design, database choices (SQL vs. NoSQL), caching strategies, load balancing, message queues, and microservices architecture. Work through common system design case studies and practice designing systems like a URL shortener, a Twitter feed, or an e-commerce platform.","shortDescription":"Weeks 3-4: System Design Concepts. Study case studies and design common systems."}
- {"title":"Behavioral Preparation","longDescription":"Week 5: Prepare for behavioral interviews. Identify key projects and experiences that demonstrate your skills in problem-solving, teamwork, leadership, and handling challenges. Practice answering common behavioral questions using the STAR method. Reflect on your motivations for joining DoorDash.","shortDescription":"Week 5: Behavioral Interview Prep. Use STAR method for past experiences."}
- {"title":"Mock Interviews and Final Review","longDescription":"Week 6: Mock interviews and review. Conduct mock interviews with peers or mentors to simulate the actual interview environment. Review your weak areas identified during practice and mock interviews. Prepare specific questions to ask the interviewers.","shortDescription":"Week 6: Mock Interviews & Review. Practice and refine answers."}

## Location differences

- {"location":"San Francisco, CA","differences":{"tips":["Be prepared to discuss your experience with microservices architecture.","Familiarize yourself with common distributed system patterns.","Highlight any experience with large-scale data processing."],"interviewFocus":["System design for distributed systems","Scalability and performance optimization","Experience with cloud platforms (AWS, GCP)"],"commonQuestions":["How would you design a system to handle real-time order updates for Dashers?","Discuss a challenging technical problem you faced and how you solved it.","Explain the trade-offs between different database solutions for a high-throughput system."]}}
- {"location":"Remote","differences":{"tips":["Provide specific examples of how you've contributed to team success.","Showcase your ability to communicate technical concepts clearly.","Emphasize your commitment to continuous learning and improvement."],"interviewFocus":["Collaboration and teamwork","Mentorship and leadership potential","Understanding of software development lifecycle"],"commonQuestions":["Describe a time you had to mentor a junior engineer.","How do you approach code reviews to ensure quality and knowledge sharing?","What are your thoughts on agile development methodologies?"]}}

## Round 1: Data Structures and Algorithms
**Type:** Technical Interview - Data Structures and Algorithms · **Difficulty:** Medium · **Duration:** 45 min
Assess core CS knowledge with coding problems.
This round focuses on your fundamental computer science knowledge. You will be asked to solve coding problems that test your understanding of data structures (e.g., arrays, linked lists, trees, graphs, hash maps) and algorithms (e.g., sorting, searching, dynamic programming). The interviewer will assess your ability to write clean, efficient, and correct code, as well as your problem-solving approach and communication skills.
**Interviewers look for:** Strong understanding of data structures and algorithms.; Ability to translate a problem into clean, efficient code.; Logical thinking and systematic approach to problem-solving.; Good communication of thought process.
**Evaluation criteria:** Correctness of the solution; Efficiency of the solution (time and space complexity); Code clarity and readability; Problem-solving approach
**Common rejection reasons:** Inability to articulate thought process clearly.; Lack of fundamental data structure and algorithm knowledge.; Poor coding practices or syntax errors.; Inability to solve problems within the given time constraints.
## Questions

- Given a binary tree, find its maximum depth.
- Implement a function to find the kth smallest element in an unsorted array.
- Write a function to check if a string is a palindrome.

## Preparation tips

- Practice coding problems on platforms like LeetCode, HackerRank.
- Focus on understanding the time and space complexity of your solutions.
- Be prepared to explain your thought process step-by-step.
- Practice writing code on a whiteboard or in a shared editor.

## Round 2: System Design
**Type:** System Design Interview · **Difficulty:** Hard · **Duration:** 60 min
Design a scalable and reliable system.
This round evaluates your ability to design scalable, reliable, and maintainable software systems. You will be presented with a high-level problem and asked to design a system to solve it. This involves discussing various components, data storage, APIs, scalability considerations, and potential bottlenecks. The interviewer will assess your understanding of distributed systems, databases, caching, and other relevant technologies.
**Interviewers look for:** Ability to design complex systems from scratch.; Knowledge of distributed systems principles.; Understanding of trade-offs in system design.; Ability to handle scale and high availability.; Clear communication of design choices.
**Evaluation criteria:** Scalability of the design; Reliability and fault tolerance; Clarity and completeness of the design; Trade-off analysis; Understanding of system components
**Common rejection reasons:** Inability to design a scalable and reliable system.; Lack of understanding of distributed systems concepts.; Poor trade-off analysis.; Not considering edge cases or failure scenarios.
## Questions

- Design a system like TinyURL.
- Design a news feed system.
- How would you design a rate limiter?

## Preparation tips

- Study system design concepts (e.g., CAP theorem, load balancing, caching, databases, message queues).
- Practice designing common systems like Twitter feed, URL shortener, or a ride-sharing service.
- Be prepared to discuss trade-offs and justify your design decisions.
- Think about scalability, availability, and performance.

## Round 3: Behavioral and Cultural Fit
**Type:** Behavioral Interview · **Difficulty:** Medium · **Duration:** 45 min
Assess behavioral competencies and cultural fit.
This round focuses on your behavioral and cultural fit. You will be asked questions about your past experiences, how you handle challenges, work with others, and your motivations. The interviewer will assess your alignment with DoorDash's core values and your potential to thrive in the company culture. Using the STAR method (Situation, Task, Action, Result) is highly recommended for answering these questions.
**Interviewers look for:** Evidence of DoorDash's core values in past experiences.; Ability to work effectively in a team.; Self-awareness and a growth mindset.; Passion for DoorDash's mission.; Good communication and interpersonal skills.
**Evaluation criteria:** Alignment with DoorDash values (e.g., Customer Obsession, Optimism, Bias for Action).; Past experiences and accomplishments.; Problem-solving and decision-making skills.; Teamwork and collaboration abilities.; Communication and interpersonal skills.; Motivation and cultural fit.
**Common rejection reasons:** Lack of self-awareness.; Inability to provide specific examples.; Negative attitude or poor interpersonal skills.; Lack of alignment with DoorDash values.; Unclear career goals.
## Questions

- Tell me about a time you failed and what you learned from it.
- Describe a situation where you had to work with a difficult colleague.
- Why are you interested in DoorDash?

## Preparation tips

- Review DoorDash's mission and values.
- Prepare examples using the STAR method for common behavioral questions.
- Be ready to discuss your strengths, weaknesses, and career aspirations.
- Show enthusiasm for the role and the company.

## Round 4: Hiring Manager Discussion
**Type:** Hiring Manager Interview · **Difficulty:** Medium · **Duration:** 30 min
Final discussion with the hiring manager.
This is typically the final round with the hiring manager. It's an opportunity for the manager to assess your overall fit for the team, discuss your career goals, and answer any remaining questions you might have. They will also gauge your understanding of the role and how you can contribute to the team's objectives. This round is also crucial for you to determine if the role and team are the right fit for you.
**Interviewers look for:** Enthusiasm for the role and team.; Clear understanding of the position.; Good communication and alignment with the manager.; Potential for growth within the team.
**Evaluation criteria:** Alignment with team's goals and vision.; Understanding of the role's responsibilities.; Candidate's questions and engagement.; Overall fit with the team and manager's expectations.
**Common rejection reasons:** Lack of alignment with team's technical direction.; Poor communication with the hiring manager.; Unrealistic salary expectations.; Lack of enthusiasm for the role or team.
## Questions

- What are your career goals for the next 3-5 years?
- What are you looking for in your next role?
- Do you have any questions for me?

## Preparation tips

- Prepare questions about the team's projects, challenges, and culture.
- Reiterate your interest and enthusiasm for the role.
- Be ready to discuss your career aspirations and how they align with the opportunity.
- Ensure you have a clear understanding of the role's expectations.