Union-Find (Disjoint Set Union): connectivity and grouping.
Union-Find answers 'are these in the same group?' almost instantly and drives connected-components, cycle detection, and clustering. Interviewers look for path compression plus union by rank for near-O(1) operations. The answer follows.
Updated Sep 2026 · Grounded in real GenAI, LLM, and AI/ML engineering interview loops and written to a senior-engineer editorial bar.
Union-Find answers 'are these in the same group?' almost instantly and drives connected-components, cycle detection, and clustering. Interviewers look for path compression plus union by rank for near-O(1) operations. The answer follows.
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.
