We introduce a quantum dynamic programming framework that allows us to directly extend to the quantum realm a large body of classical dynamic programming algorithms. The corresponding quantum dynamic programming algorithms retain the same space complexity as their classical counterpart, while achieving a computational speedup. For a combinatorial (search or optimization) problem P and an instance I of P, such a speedup can be expressed in terms of the average degree δ of the {dependency digraph} G_𝒫(I) of I, determined by a recursive formulation of P. The nodes of this graph are the subproblems of P induced by I and its arcs are directed from each subproblem to those on whose solution it relies. In particular, our framework allows us to solve the considered problems in Õ(|V(G_𝒫(I))| √δ) time. As an example, we obtain a quantum version of the Bellman-Ford algorithm for computing shortest paths from a single source vertex to all the other vertices in a weighted n-vertex digraph with m edges that runs in Õ(n√{nm}) time, which improves the best known classical upper bound when m ∈ Ω(n^{1.4}).
@InProceedings{caroppo_et_al:LIPIcs.WADS.2025.14, author = {Caroppo, Susanna and Da Lozzo, Giordano and Di Battista, Giuseppe and Goodrich, Michael T. and N\"{o}llenburg, Martin}, title = {{Quantum Speedups for Polynomial-Time Dynamic Programming Algorithms}}, booktitle = {19th International Symposium on Algorithms and Data Structures (WADS 2025)}, pages = {14:1--14:22}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-398-0}, ISSN = {1868-8969}, year = {2025}, volume = {349}, editor = {Morin, Pat and Oh, Eunjin}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.WADS.2025.14}, URN = {urn:nbn:de:0030-drops-242454}, doi = {10.4230/LIPIcs.WADS.2025.14}, annote = {Keywords: Dynamic Programming, Quantum Algorithms, Quantum Random Access Memory} }
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