Doordash iOS Engineer Interview Guide

The Phone Screening with HR in the Doordash iOS Engineer interview is generally a relaxed and informal conversation with the recruiter. The goal here is to understand you better. 

They may inquire about your background, past experiences, and your motivation for wanting to work at Doordash. As the conversation progresses, they might ask some basic iOS-related questions to gauge your knowledge in that domain. For instance, questions about your experience with Core Data, UIKit, or the App Store submission process could come up. Be prepared to discuss your relevant experience.

This interview round is usually not too challenging to pass. Ensure you have a concise elevator pitch, have reviewed your previous work experiences, and can provide a compelling answer for why you're interested in joining Doordash.

This interview is quite similar to the one which occurs for the Tinder iOS Engineer.

This one would require around 4-5 hours of your time and typically involves domain-specific tasks related to developing a relevant iOS application. 

For instance, a previous candidate was emailed a zip file that contained an Xcode project, a README, a JSON sample file, and a struct with a `getItemData()` function that has just three lines of code to load the JSON data from disk. The goal was to assess their coding skills and familiarity with iOS development.

The interview is conducted as a one-hour Zoom call with an iOS engineer from DoorDash. This is where you'll get the opportunity to go over the take-home project you've previously completed. The recruiter will make it clear during the initial call that this interview will largely revolve around discussing your assignment, so be sure to know it inside out.

Apart from the project discussion, be prepared for a deep dive into iOS development. The interview places significant emphasis on Swift, even if your prior experience is primarily in Objective-C. The reason for this is to assess your ability to quickly adapt to new technologies and still deliver a high-quality project.

So, our advice is to brush up on your Swift skills, even if you're more accustomed to Objective-C.

You can also expect theoretical questions like "Frames vs Bounds?" or "What is MVVM-bindings?" If you get through this round, you'll be invited for the onsite interview.

The onsite interview is divided into four main steps, each designed to assess different aspects of your skills and experience:

• Coding Rounds: There are two coding rounds; one involves working on the code of an existing project, and the other involves solving a domain-specific problem related to iOS development. Both of the coding rounds will happen on the laptop. Consider it an opportunity to demonstrate your problem-solving skills, understanding of iOS concepts, and your coding abilities under time constraints. It's also important to focus on code quality, maintainability, and scalability. Plus, make sure to communicate your thought process clearly to the interviewers.
• System Design: The final architecture interview is about assessing your ability to design complex software systems. You may be given a scenario or problem to solve that requires you to think about the big picture, including scalability, performance, and maintainability. You will also be expected to demonstrate your understanding of system design principles, scalability, and architecture best practices.
• Behavioural Round: This is where they get to know you better as a candidate. You can expect questions about your background, experience, and how you've handled various design challenges in the past. It's important to highlight your communication skills and teamwork abilities during this phase.

Some of these interviews can be quite lengthy, often lasting over an hour. The interviewers are looking for candidates who not only write code but can also design it properly, debug effectively, and have a good understanding of networking concepts.

Interview Questions:

• Define and explain the concept of the responder chain in the context of iOS development.
• Elaborate on the differences between Grand Central Dispatch (GCD) and Operation Queues in managing concurrent tasks in iOS development.
• What are the drawbacks of using storyboards?Explain the difference between protocols and inheritance.
• Highlight the distinctions between structs and classes.
• Discuss the concept of mutating methods in both structs and classes.
• Elaborate on the differences between unowned and weak references.
• Provide an example to illustrate the concept of a retain cycle in memory management.
• Share the disadvantages of using the Singleton design pattern.
• Explain the key differences between the Model-View-Controller (MVC) and Model-View-ViewModel (MVVM) architectural patterns.
• Clarify the distinctions between escaping and non-escaping closures in Swift.
• Define and explain the concept of the responder chain in the context of iOS development.