Number of Islands: connected components on a grid (flood fill).
A staple grid-traversal problem probing BFS/DFS flood fill and disciplined visited-marking. What interviewers watch for: viewing the grid as a graph and tallying connected components. Here is the answer.
Updated Sep 2026 · Grounded in real GenAI, LLM, and AI/ML engineering interview loops and written to a senior-engineer editorial bar.
A staple grid-traversal problem probing BFS/DFS flood fill and disciplined visited-marking. What interviewers watch for: viewing the grid as a graph and tallying connected components. Here is the answer.
Lead with where the obvious approach breaks, because that is the judgment they are screening for — most candidates jump straight to the happy path and lose the room.
Then walk the failure back through the pipeline in order, naming the one metric the customer's exec sponsor actually cares about before you propose the fix.
