Power of a pebble: Exploring and mapping directed graphs

Michael A. Bender, Antonio Fernandez, Dana Ron, Amit Sahai, Salil Vadhan

Research output: Contribution to journalConference articlepeer-review

Abstract

Exploring and mapping an unknown environment is a fundamental problem that is studied in a variety of contexts. Many works have focused on finding efficient solutions to restricted versions of the problem. In this paper, we consider a model that makes very limited assumptions about the environment and solve the mapping problem in this general setting. We model the environment by an unknown directed graph G, and consider the problem of a robot exploring and mapping G. We do not assume that the vertices of G are labeled, and thus the robot has no hope of succeeding unless it is given some means of distinguishing between vertices. For this reason we provide the robot with a `pebble' - a device that it can place on a vertex and use to identify the vertex later. In this paper we show: (1) If the robot knows an upper bound on the number of vertices then it can learn the graph efficiently with only one pebble. (2) If the robot does not know an upper bound on the number of vertices n, then Θ(log log n) pebbles are both necessary and sufficient. In both cases our algorithms are deterministic.

Original languageEnglish
Pages (from-to)269-278
Number of pages10
JournalConference Proceedings of the Annual ACM Symposium on Theory of Computing
StatePublished - 1998
Externally publishedYes
EventProceedings of the 1998 30th Annual ACM Symposium on Theory of Computing - Dallas, TX, USA
Duration: 23 May 199826 May 1998

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