School of Science, Beijing University of Posts and Telecommunications, Beijing 100876, China
Academy of Mathematics and Systems Science, Chinese Academy of Sciences, Beijing 100190, China
Beijing Institute for Scientific and Engineering Computing, Beijing University of Technology, Beijing 100124, China
School of Computer Science and Technology, Shandong Jianzhu University, Jinan 250101, China
Abstract
In this paper, we study the prize-collecting -Steiner tree (PCST) problem. We are given a graph and an integer . The graph is connected and undirected. A vertex called root and a subset called terminals are also given. A feasible solution for the PCST is a tree rooted at and connecting at least vertices in . Excluding a vertex from the tree incurs a penalty cost, and including an edge in the tree incurs an edge cost. We wish to find a feasible solution with minimum total cost. The total cost of a tree is the sum of the edge costs of the edges in and the penalty costs of the vertices not in . We present a simple approximation algorithm with the ratio of for the PCST. This algorithm uses the approximation algorithms for the prize-collecting Steiner tree (PCST) problem and the -Steiner tree (ST) problem as subroutines. Then we propose a primal-dual based approximation algorithm and improve the approximation ratio to .