Browsing by Author "Guruswami, V"

Now showing 1 - 2 of 2

The K-r-packing problem
(2001)
Guruswami, V
;
Rangan, CP
;
Chang, MS
;
Chang, GJ
;
Wong, CK
For a fixed integer r greater than or equal to 2, the K-r-packing problem is to find the maximum number of pairwise vertex-disjoint K-r's (complete graphs on r vertices) in a given graph. The K-r-factor problem asks fur the existence of a partition of the vertex set of a graph into K-r's. The K-r-packing problem is a natural generalization of the classical matching problem, but turns out to be much harder for r greater than or equal to 3 - it is known that for r greater than or equal to 3 the K-r-factor problem is NP-complete: for graphs with clique number r [16]. This paper considers the complexity of the K-r-packing problem on restricted classes of graphs. We first prove that for r greater than or equal to 3 the K-r-packing problem is NP-complete even when restrict to chordal graphs, planar graphs (for r = 3. 4 only), line graphs acid total graphs. The hardness result for K-3- packing on chordal graphs answers an open question raised in [6]. We also give (simple) polynomial algorithms for the K-3-packing and the K-r-factor problems on split graphs (this is interesting in light of the fact that K-r-packing becomes NP-complete on split graphs for r greater than or equal to 4), and for the K-r-packing problem on cographs.
The vertex-disjoint triangles problem
(1998)
Guruswami, V
;
Rangan, CP
;
Chang, MS
;
Chang, GJ
;
Wong, CK
The vertex-disjoint triangles (VDT) problem asks for a set of maximum number of pairwise vertex-disjoint triangles in a given graph G. The triangle cover problem asks for the existence of a perfect triangle packing in a graph G. It is known that the triangle cover problem is NP-complete on general graphs with clique number 3 [6]. The VDT problem is MAX SNP-hard on graphs with maximum degree four, while it can be approximated within 3/2 + epsilon, for any epsilon > 0, in polynomial time [11]. We prove that the VDT problem is NP-complete even when the input graphs are chordal, planar, line or total graphs. We present an O(m root n) algorithm for the VDT problem on split graphs and an O(n(3)) algorithm for the VDT problem on cographs. A linear algorithm for the triangle cover problem on strongly chordal graphs is also presented. Finally, the notion of packing-hardness, which may be crucial to the understanding of the difficulty of generalized matching problems, is defined.