On minimum cost edge searching

We consider the problem of finding edge search strategies of minimum cost. The cost of a search strategy is the sum of searchers used in the clearing steps of the search. One of the natural questions is whether it is possible to find a search strategy that minimizes both the cost and the number of searchers used to clear a given graph G. We call such a strategy ideal. We prove, by an example, that ideal search strategies do not exist in general. On the other hand, we provide a formula for the cost of clearing complete graphs. From our construction it follows that an ideal search strategy of a complete graph does exist and can be calculated efficiently. For general graphs G we give a polynomial-time O(logn)-approximation algorithm for finding minimum cost search strategies. We also prove that recontamination does not help to obtain minimum cost edge search strategies.