Abstract
In this work, we consider the k-Canadian Traveller Problem (k-CTP) under the learning-augmented framework proposed by Lykouris & Vassilvitskii [23]. k-CTP is a generalization of the shortest path problem, and involves a traveller who knows the entire graph in advance and wishes to find the shortest route from a source vertex s to a destination vertex t, but discovers online that some edges (up to k) are blocked once reaching them. A potentially imperfect predictor gives us the number and the locations of the blocked edges.
We present a deterministic and a randomized online algorithm for the learning-augmented k-CTP that achieve a tradeoff between consistency (quality of the solution when the prediction is correct) and robustness (quality of the solution when there are errors in the prediction). Moreover, we prove a matching lower bound for the deterministic case establishing that the tradeoff between consistency and robustness is optimal, and show a lower bound for the randomized algorithm. Finally, we prove several deterministic and randomized lower bounds on the competitive ratio of k-CTP depending on the prediction error, and complement them, in most cases, with matching upper bounds.
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Notes
- 1.
As mentioned in earlier, while a \((2k+1)\)-competitive (matching the lower bound) deterministic algorithm is known for general graph, a \((k+1)\)-competitive randomized algorithm (matching the lower bound) is only known for path-disjoint graphs.
- 2.
If the graph contains less than k disjoint paths, then choose the maximum number of paths \(l < k\) and run RandBacktrack with parameter \(l-1\). The analysis remains the same.
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This work was partially funded by the grant ANR-19-CE48-0016 from the French National Research Agency (ANR).
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Bampis, E., Escoffier, B., Xefteris, M. (2022). Canadian Traveller Problem with Predictions. In: Chalermsook, P., Laekhanukit, B. (eds) Approximation and Online Algorithms. WAOA 2022. Lecture Notes in Computer Science, vol 13538. Springer, Cham. https://doi.org/10.1007/978-3-031-18367-6_6
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