Ping Pong in Dangerous Graphs: Optimal Black Hole Search with Pure Tokens
DISC '08 Proceedings of the 22nd international symposium on Distributed Computing
Black Hole Search with Tokens in Interconnected Networks
SSS '09 Proceedings of the 11th International Symposium on Stabilization, Safety, and Security of Distributed Systems
Synchronization Helps Robots to Detect Black Holes in Directed Graphs
OPODIS '09 Proceedings of the 13th International Conference on Principles of Distributed Systems
Locating and repairing faults in a network with mobile agents
Theoretical Computer Science
Mapping an unfriendly subway system
FUN'10 Proceedings of the 5th international conference on Fun with algorithms
Time optimal algorithms for black hole search in rings
COCOA'10 Proceedings of the 4th international conference on Combinatorial optimization and applications - Volume Part II
Synchronous black hole search in directed graphs
Theoretical Computer Science
Tight bounds for scattered black hole search in a ring
SIROCCO'11 Proceedings of the 18th international conference on Structural information and communication complexity
Improving the optimal bounds for black hole search in rings
SIROCCO'11 Proceedings of the 18th international conference on Structural information and communication complexity
Black hole search with finite automata scattered in a synchronous torus
DISC'11 Proceedings of the 25th international conference on Distributed computing
Distributed security algorithms by mobile agents
ICDCN'06 Proceedings of the 8th international conference on Distributed Computing and Networking
Black hole search in directed graphs
SIROCCO'09 Proceedings of the 16th international conference on Structural Information and Communication Complexity
Periodic data retrieval problem in rings containing a malicious host
SIROCCO'10 Proceedings of the 17th international conference on Structural Information and Communication Complexity
FUN'12 Proceedings of the 6th international conference on Fun with Algorithms
Asynchronous exploration of an unknown anonymous dangerous graph with o(1) pebbles
SIROCCO'12 Proceedings of the 19th international conference on Structural Information and Communication Complexity
Locating a black hole in an un-oriented ring using tokens: the case of scattered agents
Euro-Par'07 Proceedings of the 13th international Euro-Par conference on Parallel Processing
Rendezvous of mobile agents in unknown graphs with faulty links
DISC'07 Proceedings of the 21st international conference on Distributed Computing
Fault-Tolerant exploration of an unknown dangerous graph by scattered agents
SSS'12 Proceedings of the 14th international conference on Stabilization, Safety, and Security of Distributed Systems
Exploring an unknown dangerous graph using tokens
Theoretical Computer Science
Searching for a black hole in interconnected networks using mobile agents and tokens
Journal of Parallel and Distributed Computing
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In this paper we address the problem of mobile agents searching for a highly harmful item (called a black hole) in a ring network. The black hole is a stationary process that destroys visiting agents upon their arrival without leaving any observable trace of such a destruction. The task is to have at least one surviving agent able to unambiguously report the location of the black hole. We consider different scenarios and in each situation we answer some computational as well as complexity questions. We first consider agents that start from the same home base (co-located). We prove that two such agents are necessary and sufficient to locate the black hole; in our algorithm the agents perform O(n log n) moves (where n is the size of the ring) and we show that such a bound is optimal. We also consider time complexity and show how to achieve the optimal bound of 2n - 4 units of time using n - 1 agents. We generalize our technique to establish a trade-off between time and number of agents. We then consider the case of agents that start from different home bases (dispersed) and we show that if the ring is oriented, two dispersed agents are still necessary and sufficient. Also in this case our algorithm is optimal in terms of number of moves (Θ(n log n)). We finally show that if the ring is unoriented, three agents are necessary and sufficient; an optimal algorithm follows from the oriented case.