Collision-free routing problem with restricted L-path

Document Type

Conference Article

Publication Title

Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)


We consider a variant of collision-free routing problem CRP. In this problem, we are given set C of n vehicles which are moving in a plane along a predefined directed rectilinear path. Our objective (CRP) is to find the maximum number of vehicles that can move without collision. CRP is shown to be NP-Hard by Ajaykumar et al. [1]. It was also shown that the approximation of this problem is as hard as Maximum Independent Set problem (MIS) even if the paths between a pair of vehicles intersects at most once. So we study the constrained version CCRP of CRP in which each vehicle ci is allowed to move in a directed L-Shaped Path. We prove CCRP is NP-Hard by a reduction from MIS in L-graphs, which was proved to be NP-Hard even for unit L-graph by Lahiri et al. [2]. Simultaneously, we show that any CCRP can be partitioned into collection L of L-graphs such that CCRP reduces to a problem of finding MIS in L-graph for each partition in L. Thus we show that any algorithm, that can produce a β -approximation for L-graph, would produce aβ -approximation for CCRP. We show that unit L-graphs intersected by an axis-parallel line is Co-comparable. For this problem, we propose an algorithm for finding MIS that runs in O(n2) time and uses O(n) space. As a corollary, we get a 2-approximation algorithm for finding MIS of unit L-graph that runs in O(n2) time and uses O(n) space.

First Page


Last Page




Publication Date


This document is currently not available here.