Instacart Software Engineer Interview Guide

The Phone Screen with Recruiter for Instacart is typically a 30-minute interview where they aim to get to know you better and assess both your cultural fit within the company and your technical qualifications. During this interview, you can expect a mix of basic questions about yourself and more in-depth inquiries into your professional experiences.

The conversation typically starts with introductions, and then the recruiter will go on to inquire about your current role, the size of your team, past projects and your involvement in shaping them. It's a good idea to have concise yet informative answers prepared for questions like "tell me about yourself" OR "tell me about your most successful project? OR "why do you want to join Instacart?" 

This interview is quite similar to the one which occurs for the Zomato SWE interview and the Uber SWE interview.

The real meat of the conversation comes when they start probing into the technical aspects. While they don't ask you to whiteboard anything, be prepared to delve into technical details. They'll likely want to understand the technical stack and architecture of your current project. This could involve discussing the technologies you've used, how you've implemented them, and the impact they've had on your project's success.

The technical screen is conducted opposite a senior software engineer and typically involves a 60-minute coding challenge. You'll be presented with a multi-part question (from platforms like LeetCode or HackerRank) where all the parts are given at once. This means that the different parts of the question might be interconnected and influence how you approach the problem.

The top priority in this coding challenge is to produce compilable and running code. Instacart often uses HackerRank CodePair for this purpose, which allows you to write and run your code in real-time. To prepare for this interview:

1. The key goal during this interview is to produce compilable and running code. Instacart often uses HackerRank CodePair's feature for running the code, so it's essential to make sure your code works as expected within this environment. Plus, make sure you practise asymptotic time complexity; understanding the Big O notation and optimising your algorithms is vital.
2. Be prepared to discuss and potentially code solutions related to projects listed on your resume. The interviewer may want to dive deep into your past work and how you handled technical challenges.
3. Brush up on your knowledge of data structures, especially those commonly used in software development, such as arrays, lists, and hash maps. String manipulation is a common topic in Instacart's coding interviews. So, practice tasks involving string operations, substring search, and character manipulation.

The on-site interview is quite intense, lasting around 5 hours straight with just a 30-minute break in the middle.

During this time, you'll face a series of interviews—including 2 coding challenges, 1 behaviour/bar raiser interview, and a system design interview. 

The coding portion of the interview tends to be more challenging compared to the system design and bar raiser interviews. Unlike typical LeetCode-style questions, these coding challenges are divided into 3 parts. The first part usually involves a relatively simple coding task, but the subsequent parts build upon the previous ones. The questions will be tailored for Python and Ruby on Rails—be prepared for questions related to key-value storage and retrieval, coordinate matching, and expression evaluation. 

For instance, you may be asked questions like:

• Implement a function that calculates the factorial of a given positive integer.
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One thing to note is that you might not receive extensive feedback from interviewers during the process, They may not necessarily provide hints or guidance to nudge you in the right direction (as reported by several previous candidates). So it's important to be self-reliant and think critically; explain your thought process clearly to the interviewer, even if you're stuck. 

For the system design round, you may be asked more nuanced questions like "design and white-board a database model for an Instacart-like system." Make sure you are well-versed with designing such high-level systems and have a solid grasp of trade-offs; consider issues like data storage, load balancing, and fault tolerance, scalability, reliability, and performance. Finally, be ready to explain your design choices and justify them based on the specific requirements of the problem.

As for the bar raiser, expect typical questions like "Why do you want to join Instacart?" OR "What was the most challenging project you worked on?" Here, be prepared to discuss your past experiences, both technical and non-technical. Show how you've worked as part of a team, resolved conflicts, and demonstrated leadership or problem-solving skills in previous roles. Instacart values a customer-centric approach, so highlight instances where you've gone above and beyond to satisfy customers or improve user experiences.

Participating in mock interviews with an experienced software engineer can be a highly effective way to prepare for the on-site technical/coding round.

Mock interviews provide an opportunity to simulate real interview conditions and receive feedback on your performance. The expert may ask you coding questions, provide guidance on your problem-solving approach, and offer tips on how to communicate your thought process effectively. This can help you refine your skills and ensure that you are well-prepared to tackle the real interview with confidence.

Booking a 60-minute session with an Instacart Software Software Engineer expert here.

• Implement a simple key-value storage system that allows you to set, get, and delete key-value pairs. The system should be able to handle a large number of key-value pairs efficiently.
• Given a list of coordinates (x, y), implement a function that finds all pairs of coordinates that are at a specified distance 'd' apart.
• Create a function that can evaluate mathematical expressions given as strings. The expressions can include basic arithmetic operations (+, -, *, /), parentheses, and support for variables.
• Develop a key-value datastore capable of historical value retrieval. It should handle multiple values for a single key at various timestamps. This datastore should support queries based on the key alone or the key along with a timestamp.
• Write an SQL query using a subquery that retrieves three columns: customerID, productID, and rating. Your task is to identify the top 10 products based on their ratings.
• Create a Python script for converting USD to euros. Additionally, discuss strategies for optimising API usage within this context.
• Describe a significant long-term project you managed during your previous employment.
• Design a system that can fetch updated information from an API and deliver it to the user.

At the end of the interview day, there's a 15-minute chat with an engineer where you can ask any questions you have about Instacart. Make sure you prepare questions in advance that demonstrate your genuine interest in Instacart and the role—ask about the company culture, internal team dynamics, the projects you might work on, etc.