1,879 research outputs found
Max-Leaves Spanning Tree is APX-hard for Cubic Graphs
We consider the problem of finding a spanning tree with maximum number of
leaves (MaxLeaf). A 2-approximation algorithm is known for this problem, and a
3/2-approximation algorithm when restricted to graphs where every vertex has
degree 3 (cubic graphs). MaxLeaf is known to be APX-hard in general, and
NP-hard for cubic graphs. We show that the problem is also APX-hard for cubic
graphs. The APX-hardness of the related problem Minimum Connected Dominating
Set for cubic graphs follows
On the Complexity of the Single Individual SNP Haplotyping Problem
We present several new results pertaining to haplotyping. These results
concern the combinatorial problem of reconstructing haplotypes from incomplete
and/or imperfectly sequenced haplotype fragments. We consider the complexity of
the problems Minimum Error Correction (MEC) and Longest Haplotype
Reconstruction (LHR) for different restrictions on the input data.
Specifically, we look at the gapless case, where every row of the input
corresponds to a gapless haplotype-fragment, and the 1-gap case, where at most
one gap per fragment is allowed. We prove that MEC is APX-hard in the 1-gap
case and still NP-hard in the gapless case. In addition, we question earlier
claims that MEC is NP-hard even when the input matrix is restricted to being
completely binary. Concerning LHR, we show that this problem is NP-hard and
APX-hard in the 1-gap case (and thus also in the general case), but is
polynomial time solvable in the gapless case.Comment: 26 pages. Related to the WABI2005 paper, "On the Complexity of
Several Haplotyping Problems", but with more/different results. This papers
has just been submitted to the IEEE/ACM Transactions on Computational Biology
and Bioinformatics and we are awaiting a decision on acceptance. It differs
from the mid-August version of this paper because here we prove that 1-gap
LHR is APX-hard. (In the earlier version of the paper we could prove only
that it was NP-hard.
Flip Distance Between Triangulations of a Planar Point Set is APX-Hard
In this work we consider triangulations of point sets in the Euclidean plane,
i.e., maximal straight-line crossing-free graphs on a finite set of points.
Given a triangulation of a point set, an edge flip is the operation of removing
one edge and adding another one, such that the resulting graph is again a
triangulation. Flips are a major way of locally transforming triangular meshes.
We show that, given a point set in the Euclidean plane and two
triangulations and of , it is an APX-hard problem to minimize
the number of edge flips to transform to .Comment: A previous version only showed NP-completeness of the corresponding
decision problem. The current version is the one of the accepted manuscrip
On Approximability of Steiner Tree in -metrics
In the Continuous Steiner Tree problem (CST), we are given as input a set of
points (called terminals) in a metric space and ask for the minimum-cost tree
connecting them. Additional points (called Steiner points) from the metric
space can be introduced as nodes in the solution. In the Discrete Steiner Tree
problem (DST), we are given in addition to the terminals, a set of facilities,
and any solution tree connecting the terminals can only contain the Steiner
points from this set of facilities. Trevisan [SICOMP'00] showed that CST and
DST are APX-hard when the input lies in the -metric (and Hamming
metric). Chleb\'ik and Chleb\'ikov\'a [TCS'08] showed that DST is NP-hard to
approximate to factor of in the graph metric (and
consequently -metric). Prior to this work, it was unclear if CST
and DST are APX-hard in essentially every other popular metric! In this work,
we prove that DST is APX-hard in every -metric. We also prove that CST
is APX-hard in the -metric. Finally, we relate CST and DST,
showing a general reduction from CST to DST in -metrics. As an
immediate consequence, this yields a -approximation polynomial time
algorithm for CST in -metrics.Comment: Abstract shortened due to arxiv's requirement
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