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Towards optimal and expressive kernelization for $$d$$-hitting set. (English) Zbl 1314.68167
Summary: A sunflower in a hypergraph is a set of hyperedges pairwise intersecting in exactly the same vertex set. Sunflowers are a useful tool in polynomial-time data reduction for problems formalizable as $$d$$-Hitting Set, the problem of covering all hyperedges (whose cardinality is bounded from above by a constant $$d$$) of a hypergraph by at most $$k$$ vertices. Additionally, in fault diagnosis, sunflowers yield concise explanations for “highly defective structures”.
We provide a linear-time algorithm that, by finding sunflowers, transforms an instance of $$d$$-Hitting Set into an equivalent instance comprising at most $$O(k^d)$$ hyperedges and vertices. In terms of parameterized complexity, we show a problem kernel with asymptotically optimal size (unless $$\operatorname {coNP}\subseteq\operatorname {NP/poly}$$) and provide experimental results that show the practical applicability of our algorithm.
Finally, we show that the number of vertices can be reduced to $$O(k^{d-1})$$ with additional processing in $$O(k^{1.5d})$$ time – nontrivially combining the sunflower technique with problem kernels due to Abu-Khzam and Moser.

##### MSC:
 68Q25 Analysis of algorithms and problem complexity 05C65 Hypergraphs 05C85 Graph algorithms (graph-theoretic aspects)
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##### References:
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