Decision Making and Analysis for Unexpected Road Blockages

The unexpected road blockage problem (URBP for short) is considered for the case when some blockages occur on the road at certain times and such blockages would be revealed only upon reaching them. Papadimitriou and Yarmakakis proved that devising a strategy that guarantees a given competitive ratio is PSPACE-complete if the number of edges that might be blocked is not fixed; Bar-noy and Schieber considered the deterministic and stochastic variations of the recoverable-UP,BP in the worst-case criterion. In this paper, we present an offline algorithm for the recoverable-URBP optimal solution and the complexity of the algorithm is O(n(2)) (n is the number of nodes). Two online strategies, waiting strategy and the Greedy strategy, are proposed and the competitive ratios of the two strategies are given. Furthermore, we compare the two strategies based on competitive ratio analysis.