Tree exploration with logarithmic memory

  • Authors:

  • Leszek Gasieniec;Andrzej Pelc;Tomasz Radzik;Xiaohui Zhang

  • Affiliations:

  • The University of Liverpool, Liverpool, United Kingdom;Université du Québec en Outaouais, Gatineau, Québec, Canada;King's College, London, United Kingdom;The University of Liverpool, Liverpool, United Kingdom

  • Venue:
  • SODA '07 Proceedings of the eighteenth annual ACM-SIAM symposium on Discrete algorithms
  • Year:
  • 2007

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Abstract

We consider the task of network exploration by a mobile agent (robot) with small memory. The agent has to traverse all nodes and edges of a network (represented as an undirected connected graph), and return to the starting node. Nodes of the network are unlabeled and edge ports are locally labeled at each node. The agent has no a priori knowledge of the topology of the network or of its size, and cannot mark nodes in any way. Under such weak assumptions, cycles in the network may prevent feasibility of exploration, hence we restrict attention to trees. We present an algorithm to accomplish tree exploration (with return) using O(log n)-bit memory for all n-node trees. This strengthens the result from [15], where O(log2 n)-bit memory was used for tree exploration, and matches the lower bound on memory size proved there.