Forced pairs in A-Stick graphs

TL;DR

This paper characterizes A-Stick graphs using forced pairs, provides an efficient recognition algorithm, and explores segment length minimization in Stick graph representations.

Contribution

It introduces a characterization of A-Stick graphs with forced pairs and offers a faster recognition algorithm, improving upon previous methods.

Findings

Recognition algorithm runs in O(|A|+|B|+|E|) time.

Characterization of A-Stick graphs using forced pairs.

Partial results on minimizing total segment length.

Abstract

A Stick graph G=(A\cup B, E) is the intersection graph of a set A of horizontal segments and a set B of vertical segments in the plane, whose left and respectively bottom endpoints lie on the same ground line with slope -1. These endpoints are respectively called A-origins and B-origins. When a total order is provided for the A-origins, the resulting graphs are called A-Stick graphs. In this paper, we propose a characterization of the class of A-Stick graphs using forced pairs, which are pairs of segments in B with the property that only one left-to-right order of their origins is possible on the ground line. We deduce a recognition algorithm for A-Stick graphs running in O(|A|+|B|+|E|) time, thus improving the running time of O(|A|\cdot |B|) of the best current algorithm. We also introduce the problem of finding, for a Stick graph, a representation using segments of minimum total length. The canonical order on the A- and B-origins, output by our recognition algorithm, allows us to obtain partial results on this problem.