Priority evacuation from a disk: The case of n ≥ 4

J. Czyzowicz, K. Georgiou, R. Killick, E. Kranakis, D. Krizanc, L. Narayanan, J. Opatrny, S. Shende

Research output: Contribution to journalArticlepeer-review


We introduce and study a new search-type problem with (n+1)-robots on a disk. The searchers (robots) all start from the center of the disk, have unit speed, and can communicate wirelessly. The goal is for a distinguished robot (the queen) to reach and evacuate from an exit that is hidden on the perimeter of the disk in as little time as possible. The remaining n robots (servants) are there to facilitate the queen's objective and are not required to reach the hidden exit. We provide upper and lower bounds for the time required to evacuate the queen from a unit disk. Namely, we propose an algorithm specifying the trajectories of the robots which guarantees evacuation of the queen in time always better than [Formula presented] for n≥4 servants. We also demonstrate that for n≥4 servants the queen cannot be evacuated in time less than [Formula presented].

Original languageAmerican English
Pages (from-to)91-102
Number of pages12
JournalTheoretical Computer Science
StatePublished - Dec 18 2020

ASJC Scopus subject areas

  • Theoretical Computer Science
  • Computer Science(all)


  • Disk
  • Evacuation
  • Exit
  • Group Search
  • Mobile Robots
  • Priority
  • Queen
  • Servants
  • Wireless Communication


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