Approximation algorithms for non-sequential star packing problems

TL;DR

This paper introduces improved approximation algorithms for complex star packing problems in graphs, achieving better solutions for NP-hard cases through local search methods.

Contribution

It presents new approximation algorithms with improved ratios for $k^+$-star and $k^-/t$-star packing problems, advancing the state of the art.

Findings

Achieves a $(1 + rac{k^2}{2k+1})$-approximation for $k^+$-star packing when $k \\ge 3$.

Provides a $rac{3}{2}$-approximation for $k^+$-star packing when $k=2$.

Develops a $(1 + rac{1}{t + 1 + 1/k})$-approximation for $k^-/t$-star packing for $k > t \\ge 2$.

Abstract

For a positive integer $k \ge 1$, a $k$-star ($k^+$-star, $k^-$-star, respectively) is a connected graph containing a degree-$\ell$ vertex and $\ell$ degree-$1$ vertices, where $\ell = k$ ($\ell \ge k$, $1 \le \ell \le k$, respectively). The $k^+$-star packing problem is to cover as many vertices of an input graph $G$ as possible using vertex-disjoint $k^+$-stars in $G$; and given $k > t \ge 1$, the $k^-/t$-star packing problem is to cover as many vertices of $G$ as possible using vertex-disjoint $k^-$-stars but no $t$-stars in $G$. Both problems are NP-hard for any fixed $k \ge 2$. We present a $(1 + \frac {k^2}{2k+1})$- and a $\frac 32$-approximation algorithms for the $k^+$-star packing problem when $k \ge 3$ and $k = 2$, respectively, and a $(1 + \frac 1{t + 1 + 1/k})$-approximation algorithm for the $k^-/t$-star packing problem when $k > t \ge 2$. They are all local search algorithms and they improve the best known approximation algorithms for the problems, respectively.