Grids & Graph Search

Most OpenAI coding rounds ask you to build something, but pure algorithm questions still come up in two places. The HackerRank online assessment gives you about 110 minutes for two questions with the camera on, and it's mostly given to new-grad, non-US and Solutions candidates. Some candidates also get a live DSA round. Grid problems come up in both.

The grid problems don't need unusual algorithms. Each one has a slow version that passes the samples and then times out on a large hidden grid, like running one search per source, comparing regions cell by cell, or rescanning every k-by-k block. Nobody is there to answer questions on an assessment, so you have to work out the faster approach from the constraints. The faster approach usually does the shared work once. You put every source in one queue so the spread runs as a single search, or you turn each region into a key you can hash so matching becomes a set lookup. A two-dimensional window splits into two one-dimensional sweeps. After that, each cell gets touched a constant number of times.

OpenAIPremium lesson · Coding round

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