Counting matchings of size k is # W[1]-hard

  • Authors:
  • Radu Curticapean

  • Affiliations:
  • Dept. of Computer Science, Saarland University, Germany

  • Venue:
  • ICALP'13 Proceedings of the 40th international conference on Automata, Languages, and Programming - Volume Part I
  • Year:
  • 2013

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Abstract

We prove $\sharp$W[1]-hardness of the following parameterized counting problem: Given a simple undirected graph G and a parameter k∈ℕ, compute the number of matchings of size k in G. It is known from [1] that, given an edge-weighted graph G, computing a particular weighted sum over the matchings in G is $\sharp$W[1]-hard. In the present paper, we exhibit a reduction that does not require weights. This solves an open problem from [5] and adds a natural parameterized counting problem to the scarce list of $\sharp$W[1]-hard problems. Since the classical version of this problem is well-studied, we believe that our result facilitates future $\sharp$W[1]-hardness proofs for other problems.