Doordash

Assessment Rubric Overview: "Unique Shapes" Problem

Core Competencies and Skills Evaluated

This problem evaluates a candidate's proficiency in algorithm design, particularly in grid traversal and pattern recognition. Candidates are expected to demonstrate:

• Grid Traversal Techniques: Efficiently navigating 2D grids using algorithms like Depth-First Search (DFS) or Breadth-First Search (BFS) to identify connected components.

• Normalization of Shapes: Developing methods to standardize island shapes, such as translating all land cells to a common reference point, to facilitate accurate comparison.

• Handling Rotations and Reflections: Implementing algorithms that can detect and account for all possible orientations of an island, ensuring that identical shapes are recognized regardless of their rotation or reflection.

Behavioral Traits and Problem-Solving Approaches Assessed

Interviewers will evaluate the following behavioral traits:

• Analytical Thinking: The ability to break down complex problems into manageable sub-problems and systematically address each component.

• Attention to Detail: Ensuring that all edge cases, such as islands with varying sizes or irregular shapes, are considered and handled appropriately.

• Adaptability: Demonstrating flexibility in approach, especially when transitioning from Part 1 to Part 2 of the problem, which introduces additional complexity.

Candidates should articulate their thought process clearly, justify their chosen methods, and be open to feedback and alternative solutions.

Assessment Process Expectations

The interview process at DoorDash typically involves multiple stages, including:

1. Initial Screening: A recruiter conducts a phone interview to assess the candidate's background and motivation.

2. Technical Assessment: This may include coding challenges, take-home assignments, or live coding sessions focusing on problem-solving skills.

3. On-Site Interviews: Multiple rounds covering technical questions, system design, and behavioral interviews.

Candidates can expect a structured process with clear communication regarding each stage. However, some feedback indicates that the process can be lengthy, with delays in communication. For instance, one candidate mentioned that the interview process was "extremely slow," taking about 2.5 months, and that the recruiters seemed "extremely not interested in talking to you." (glassdoor.com)

Preparation Recommendations

To prepare effectively for this type of problem:

• Master Grid-Based Algorithms: Practice problems involving DFS and BFS on 2D grids to build a strong foundation.

• Understand Shape Normalization: Study techniques for translating and rotating shapes to a standard form for comparison.

• Explore Symmetry Detection: Learn methods to identify and account for rotational and reflective symmetries in shapes.

• Review Past Interview Experiences: Engage with platforms like Glassdoor to gain insights into DoorDash's interview questions and candidate experiences. One candidate advised understanding the role and DoorDash’s business model, preparing for behavioral questions, and being ready to discuss past experiences using the STAR method. (glassdoor.com)

Evaluation Criteria and Technical Concepts

Candidates should demonstrate:

• Algorithmic Efficiency: Solutions that are both time and space efficient, capable of handling large grids within reasonable time limits.

• Correctness: Accurate identification and counting of unique island shapes, with thorough testing against various test cases.

• Clarity of Code: Well-organized and readable code, with appropriate comments and documentation.

A solid understanding of computational geometry and combinatorics will be beneficial.

DoorDash-Specific Expectations and Cultural Fit Considerations

DoorDash values candidates who:

• Embrace Innovation: Demonstrate creativity in problem-solving and a willingness to explore new approaches.

• Collaborate Effectively: Showcase strong communication skills and the ability to work well in team settings.

• Align with Company Values: Exhibit a passion for DoorDash's mission and a commitment to delivering high-quality solutions.

Understanding and aligning with DoorDash's culture will be advantageous during the interview process. One candidate noted that DoorDash places a strong emphasis on cultural fit and advised being ready to discuss past experiences, how you handle challenges, teamwork, and adaptability. (glassdoor.com)