Instacart Senior Software Engineer Interview Experience — Fast Coding and a Difficult Bar Raiser

The virtual onsite had two coding rounds, one design round, and one bar-raiser round.

The coding questions were ones from interview reports, and easier than the versions on the forum. I breezed through both.

For the calculate-expression question, the interviewer said in part two that there would always be spaces around the +, =, and - signs, so parsing was straightforward. In part three, the only possible type of error was a cycle.

For the shopping question:

Part one returned a string along the lines of total unit=, total price=, with the price to two decimal places. If the input item list contained an invalid element, that item should be ignored. Possible errors included a negative price or quantity, or an item string missing required information such as the name, SKU, or quantity.

Part two calculated the best price for each item after applying promotions. The final output was the sum of all the items' best prices, again to two decimal places.

Part three was a sorting problem, ordered by aisle number. The output was a string such as Apple (aisle 1), ice cream (aisle 8) or Apple (aisle 11), ice cream (aisle 1). Frozen items always had to come last.

The design question was an inventory system. There isn't much else to say about that round: mainly consistency, avoiding overselling, and reserving items when they are added to a cart. The focus was mostly on the database: explain locking, avoiding race conditions, deadlocks, and so on. The follow-up was what to do if average TPS scaled up tenfold.

The bar-raiser round was stiff, and I feel that this was where I failed. It wasn't Amazon's usual behavioral format of "tell me about a time you XXX". It was more about covering all the behavioral questions through one project. The interviewer was a senior manager. After we introduced ourselves, he asked me to describe a project with the most impact and the greatest challenges, then kept asking questions. He wanted details showing leadership, mentorship, collaboration, technical challenges, design trade-offs, and conflicts with other people.

I really hadn't prepared this part very well. The project I talked about wasn't my most recent one, and I couldn't remember some details.

The most annoying part was that the interviewer kept nodding furiously while I talked, but not at the right moments, which really disrupted my rhythm. At the end, he asked whether I had a story about conflict with someone else. I said yes, on another project, but before I could finish, he interrupted and insisted that I continue with the original project. I said the collaboration on that project had gone pretty well later on, and he looked dissatisfied.

Sigh. 😑 I was only interviewing for an Instacart Senior 1 position. Did I really have to turn into Superman and save the planet?

Anyway, I'm job hunting full-time now and have had so many rejections that I'm numb. I'm open to both the US and Canada. 😭