Comments cont.
- if problem is generalization of known NP-complete problem, reduction is usually easy.
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Example: Set Cover
- given U, set of elements, and collection S1, S2,.., Sn of subsets of U, and an integer k
- determine if there is a subset W of U of size at most k that intersects ever set Si
Reduction from Vertex Cover
- U set of vertices
- Si is ith edge