Heaps & Intervals

This band shows up wherever a problem is about time windows or about the best few of a crowd, which at Instacart is most of the logistics layer. Delivery slots, shopper shifts, and the batches a dispatcher builds are all intervals on a clock. Offering a batch to the nearest few shoppers, or ranking the busiest stores in a region, is a top-K question. Neither shape is a large slice of the coding rounds on its own, but together they cover the scheduling and ranking work that the grocery domain leans on, so both are worth having ready.

There is no hidden trick to decode here. These are canonical problems asked close to how you already know them, wrapped in an orders-and-shoppers story. The pressure is the one Instacart applies everywhere: the code has to compile and clear the hidden tests, and the interviewer expects the time and space cost named. A version that only handles the tidy case is not enough, because a staged follow-up is usually waiting, and it lands on your own code rather than a fresh prompt. A clean sweep or a capped heap you can write without fumbling buys you the room to take that next step.

The Instacart angle

Order batching is an interval problem before it is anything else. A dispatcher groups nearby orders that share an overlapping delivery window into one trip, so a shopper picks several customers' groceries on a single run through the store. Deciding which windows can ride together is exactly the merge-overlapping-intervals move: sort the windows by start, then fold each one that touches the running window into it. The batch is the merged span. Once you see the delivery slot as an interval on a clock, the batching question turns into the standard sweep, and the marketplace framing sits lightly on top of it.

InstacartPremium lesson · Coding round

The 4 Instacart problems are below.

1. 1A Premium questionCoding · Medium
2. 2A Premium questionCoding · Medium
3. 3A Premium questionCoding · Medium

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