The binary identification problem for weighted trees

  • Authors:
  • Ferdinando Cicalese;Tobias Jacobs;Eduardo Laber;Caio Valentim

  • Affiliations:
  • University of Salerno, Italy;NEC Laboratories Europe, Germany;PUC, Rio de Janeiro, Brazil;PUC, Rio de Janeiro, Brazil

  • Venue:
  • Theoretical Computer Science
  • Year:
  • 2012

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Abstract

The Binary Identification Problem for weighted trees asks for the minimum cost strategy (decision tree) for identifying a vertex in an edge weighted tree via testing edges. Each edge has assigned a different cost, to be paid for testing it. Testing an edge e reveals in which component of T-e lies the vertex to be identified. We give a complete characterization of the computational complexity of this problem with respect to both tree diameter and degree. In particular, we show that it is strongly NP-hard to compute a minimum cost decision tree for weighted trees of diameter at least 6, and for trees having degree three or more. For trees of diameter five or less, we give a polynomial time algorithm. Moreover, for the degree 2 case, we significantly improve the straightforward O(n^3) dynamic programming approach, and provide an O(n^2) time algorithm. Finally, this work contains the first approximate decision tree construction algorithm that breaks the barrier of factor logn.