Exact algorithms for exact satisfiability and number of perfect matchings

  • Authors:
  • Andreas Björklund;Thore Husfeldt

  • Affiliations:
  • Department of Computer Science, Lund University, Lund, Sweden;Department of Computer Science, Lund University, Lund, Sweden

  • Venue:
  • ICALP'06 Proceedings of the 33rd international conference on Automata, Languages and Programming - Volume Part I
  • Year:
  • 2006

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Abstract

We present exact algorithms with exponential running times for variants of n-element set cover problems, based on divide-and-conquer and on inclusion–exclusion characterisations. We show that the Exact Satisfiability problem of size l with m clauses can be solved in time 2mlO(1) and polynomial space. The same bounds hold for counting the number of solutions. As a special case, we can count the number of perfect matchings in an n-vertex graph in time 2nnO(1) and polynomial space. We also show how to count the number of perfect matchings in time O(1.732n) and exponential space. Using the same techniques we show how to compute Chromatic Number of an n-vertex graph in time O(2.4423n) and polynomial space, or time O(2.3236n) and exponential space.