Collective tree exploration

Pierre Fraigniaud, Leszek Gasieniec, Dariusz R. Kowalski, Andrzej Pelc

Research output: Contribution to journalArticlepeer-review

113 Scopus citations


An n-node tree has to be explored by k mobile agents (robots), starting in its root. Every edge of the tree must be traversed by at least one robot, and exploration must be completed as fast as possible. Even when the tree is known in advance, scheduling optimal collective exploration turns out to be NP-hard. We investigate the problem of distributed collective exploration of unknown trees. Not surprisingly, communication between robots influences the time of exploration. Our main communication scenario is the following: robots can communicate by writing at the currently visited node previously acquired information, and reading information available at this node. We construct an exploration algorithm whose running time for any tree is only O(k/ log k) larger than optimal exploration time with full knowledge of the tree. (We say that the algorithm has overhead O(k/ log k)). On the other hand we show that, in order to get overhead sublinear in the number of robots, some communication is necessary. Indeed, we prove that if robots cannot communicate at all, then every distributed exploration algorithm works in time Ω(k) larger than optimal exploration time with full knowledge, for some trees.

Original languageEnglish (US)
Pages (from-to)166-177
Number of pages12
JournalLecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)
Issue number3
StatePublished - Jan 1 2004
Externally publishedYes


  • Algorithm
  • Collective graph exploration
  • Mobile agent
  • Robot
  • Tree

ASJC Scopus subject areas

  • Theoretical Computer Science
  • Computer Science(all)


Dive into the research topics of 'Collective tree exploration'. Together they form a unique fingerprint.

Cite this