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Capacitated dynamic programming: faster knapsack and graph algorithms. (English) Zbl 1552.68373

Baier, Christel (ed.) et al., 46th international colloquium on automata, languages, and programming, ICALP 2019, Patras, Greece, July 9–12, 2019. Proceedings. Wadern: Schloss Dagstuhl – Leibniz-Zentrum für Informatik. LIPIcs – Leibniz Int. Proc. Inform. 132, Article 19, 13 p. (2019).
Summary: One of the most fundamental problems in Computer Science is the . Given a set of \(n\) items with different weights and values, it asks to pick the most valuable subset whose total weight is below a capacity threshold \(T\). Despite its wide applicability in various areas in Computer Science, , and Finance, the best known running time for the problem is \(O(Tn)\). The main result of our work is an improved algorithm running in time \(O(TD)\), where \(D\) is the number of distinct weights. Previously, faster runtimes for Knapsack were only possible when both weights and values are bounded by \(M\) and \(V\) respectively, running in time \(O(nMV)\) [D. Pisinger, J. Algorithms 33, No. 1, 1–14 (1999; Zbl 0951.90047)]. In comparison, our algorithm implies a bound of \(O(nM^2)\) without any dependence on \(V\), or \(O(nV^2)\) without any dependence on \(M\). Additionally, for the unbounded Knapsack problem, we provide an algorithm running in time \(O(M^2)\) or \(O(V^2)\). Both our algorithms match recent conditional lower bounds shown for the Knapsack problem [M. Cygan et al., LIPIcs – Leibniz Int. Proc. Inform. 80, Article 22, 15 p. (2017; Zbl 1441.68070); M. Künnemann et al., ibid. 80, Article 21, 15 p. (2017; Zbl 1441.68078)].
We also initiate a systematic study of general capacitated dynamic programming, of which Knapsack is a core problem. This problem asks to compute the maximum weight path of length \(k\) in an edge- or node-weighted . In a graph with \(m\) edges, these problems are solvable by dynamic programming in time \(O(km)\), and we explore under which conditions the dependence on \(k\) can be eliminated. We identify large classes of graphs where this is possible and apply our results to obtain linear time algorithms for the problem of \(k\)-sparse \(\Delta\)-separated sequences. The main technical innovation behind our results is identifying and exploiting concavity that appears in relaxations and subproblems of the tasks we consider.
For the entire collection see [Zbl 1414.68003].

MSC:

68W05 Nonnumerical algorithms
05C85 Graph algorithms (graph-theoretic aspects)
68W40 Analysis of algorithms
90C27 Combinatorial optimization
90C39 Dynamic programming

References:

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