Instacart Interview Questions — Page 8

Instacart·Software Engineer·Technical Phone Screen

May 2026

Instacart software engineer interview that was basically a design discussion around a bus boarding simulation. Not a typical coding round, more of a 'talk through your choices and defend them' kind of session. Went deeper than I expected into production concerns.

You have a queue of people, each with a priority flag, and a bus with fixed capacity. Priority passengers board first in arrival order, then non-priority fill remaining seats. How would you implement this, and why did you choose that approach over alternatives like a two-queue one-pass strategy?
How would you adapt this boarding implementation for production use, specifically around thread safety if multiple boarding gates are running concurrently?
Over a long horizon with repeated boarding events, how would you prevent non-priority passengers from being perpetually starved by priority passengers?
How would you extend this design to support more than two priority levels?
What observability or metrics would you add to this system in production, and how would you handle input validation and errors?
How would you approach testing this boarding system?

“I went with a two-pass partition: first sweep collects priority people, second fills from non-priority up to capacity.”

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Instacart·Software Engineer·Technical Phone Screen

May 2026

Went through a technical phone screen for a software engineer role at Instacart. It was a graph problem dressed up as a math problem, which I thought was a clever framing.

You're given a list of equations like A / B = k, where each equation is a pair of variables and a numeric result. Given a set of queries asking for the value of C / D, evaluate each one using the known equations. Return -1.0 for any query that can't be determined.

“My first instinct was to treat it as a pure math problem and I wasted probably two minutes going down that path before realizing the variables form a graph.”

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Instacart·Data Scientist·Technical Phone Screen

May 2026

Instacart data science interview with a pretty gnarly experiment design question that covered sample sizing, sequential testing, and variance reduction all in one prompt. Felt more like a stats exam than a conversation.

Given a baseline same-day delivery attach rate of 22%, a minimum detectable relative lift of 5%, standard alpha and power settings, and 120k daily eligible checkouts (with only 20% of site traffic qualifying and strong Sunday variation), calculate the required sample size per arm and convert that to calendar days while accounting for day-of-week seasonality and a 10% cluster correlation from households.
Design a peeking-safe monitoring plan for this experiment using something like group sequential testing or alpha spending functions, and explain how that approach changes the expected experiment duration compared to a fixed-horizon design.
If the attach rate metric is especially volatile on Sundays, how would you use stratified randomization or CUPED to reduce variance, and can you quantify the expected variance reduction and its effect on how long the experiment needs to run?

“This took me way longer than it should have.”

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Instacart·Data Scientist·Onsite - Behavioral / Leadership

Jun 2026

Behavioral round at Instacart for a Data Scientist role, focused almost entirely on one big leadership question about cross-functional work under pressure. The question had a lot of moving parts and felt more like a PM interview than a DS one.

Tell me about a time you led a cross-functional initiative where the requirements were unclear and you were under serious time pressure. Walk me through how you scoped it, aligned stakeholders, kept the conversation on track, and what the measurable result was.

“This one is deceptively heavy.”

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Instacart·Software Engineer·Technical Phone Screen

Jun 2026

Coding screen for a software engineer role at Instacart. The problem looked like a file parsing puzzle at first glance but kept growing in scope as the interviewer added constraints.

You're given a file path to a text file. The file has an index line like [x, y] followed by a grid of characters where the origin is at the bottom-left. Return the character at coordinate (x, y). Then extend your solution to handle multiple index-matrix blocks in the same file: read each character, prepend it to a password string based on its index order, and return the password. If there are multiple passwords in the file, stop after completing the first one.

“The first part wasn't bad, just coordinate lookup with some off-by-one anxiety around the lower-left origin.”

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Instacart·Software Engineer·Onsite - Behavioral / Leadership

Jun 2026

Behavioral round at Instacart for a software engineer role. Four questions, all pretty standard STAR-style prompts, but a couple of them pushed harder than I expected on the specifics of trade-offs and failure.

Tell me about a time you ran into a tooling or platform limitation and still shipped. What trade-offs did you accept and how did you reduce risk?
Describe a project you owned from start to finish under a tight deadline. How did you decide what to cut and how did you keep stakeholders in the loop?
Walk me through a conflict you had with a teammate or stakeholder. How did it get resolved?
Tell me about a meaningful failure. What did you learn and what did you actually change about how you work afterward?

“This one tripped me up a bit because I kept wanting to jump to the solution before explaining why the constraint actually mattered.”

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Instacart·Machine Learning Engineer·Technical Phone Screen

Jun 2026

Coding round for an ML Engineer role at Instacart. Pretty standard binary search problem but the O(log n) constraint is what makes it interesting, so if you're prepping for this company make sure your binary search fundamentals are solid.

Given a sorted array of integers, find the first and last positions of a target value. Return [-1, -1] if the target doesn't exist. Your solution must run in O(log n) time.

“The naive approach is obvious and they explicitly block it with the complexity requirement.”

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Instacart·Software Engineer·Onsite - System Design / Architecture

Jun 2026

System design round at Instacart for a software engineering role. The question was a deep catalog service design covering schema, APIs, caching, and scaling. Pretty brutal in scope but also kind of interesting if you're into data modeling.

Design a product catalog service for a large e-commerce or grocery platform. The catalog needs a hierarchical category tree using a self-referential table, support for products belonging to multiple categories, and flexible product variants with attributes. Walk through APIs, schema, subtree query strategies, caching, scaling to 10M products, and data integrity.
How would you design the API layer for this catalog service, including product and category CRUD, hierarchy operations like moving a category or getting breadcrumbs, variant management, and async bulk import with job tracking?
Compare adjacency lists with recursive CTEs, materialized paths, and closure tables for querying category subtrees and breadcrumbs. What are the read/write trade-offs and when would you choose each?
How would you handle caching, cache invalidation, and keeping a denormalized search index consistent with the primary database in this catalog service?
How would this catalog service scale to around 10 million products at roughly 1,000 read requests per second, given that the workload is heavily read-oriented?
How do you prevent cycles in a self-referential category hierarchy, and how would you handle schema changes to this service without downtime?

“This was a lot.”

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Instacart·Software Engineer·Technical Phone Screen

Jun 2026

Instacart gave me a software engineer interview built around a ~10,000-line Python bus simulation codebase. The whole thing was about navigating unfamiliar code fast, making targeted edits, and designing a new metric from scratch. Weird format but kind of interesting once I got into it.

Given a large unfamiliar codebase, can you use an AI coding assistant to quickly locate where specific logic lives and explain what a given class is responsible for?
Make a small, targeted modification to the simulation code in the unfamiliar codebase.
Design and implement a new efficiency metric for the bus simulation. Justify your choice and integrate it into the existing code.

“This part was less stressful than I expected.”

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Instacart·Data Scientist·Hiring Manager Screen

Jun 2026

Interviewed for a Data Scientist role at Instacart and got hit with a pretty intense hiring manager screen that felt more like a strategic debrief than a standard intro call. A lot of it was about motivation and fit, but they dug deeper than I expected on the 'why Instacart' angle specifically.

Why Instacart over competitors like DoorDash or Uber Eats, or even your current company? Can you name two or three Instacart-specific product or market dynamics that match your background, and roughly quantify what you could deliver in the first six months?
What's pulling you toward Instacart and what's pushing you away from your current role? And what would need to change at your current company for you to stay?
If we called your current manager right now, what constructive criticism would they give about you, and what have you actually done about it?
Do you have any non-compete or notice period constraints, and when could you realistically start?

“This one tripped me up more than I expected.”

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