Prof. Dr. Tobias Friedrich


Two Papers accepted at ICALP and PODS

Recently, two papers by our group members have been accepted for publication: Together with a group of researchers from various universities, Pascal Lenzner wrote the paper Solving Woeginger's Hiking Problem: Wonderful Partitions in Anonymous Hedonic Games for the International Colloquium on Automata, Languages and Programming (ICALP), taking place on 8-12 July in Tallinn, Estonia. A decade ago, Gerhard Woeginger posed an open problem that became well-known as "Woeginger's Hiking Problem": Consider a group of people that want to go hiking; everyone expresses preferences over the size of their hiking group as an integer interval. Is it possible to efficiently assign the hikers to a set of subgroups so that every person approves the size of their assigned subgroup? The problem is also known as efficiently deciding if an instance of an anonymous Hedonic Game with interval approval preferences admits a wonderful partition. This paper resolves the open problem in the affirmative by presenting a polynomial-time algorithm. Moreover, the paper proposes natural, more demanding extensions of the problem, e.g., maximizing the number of satisfied participants and variants with single-peaked preferences, and shows that they are also efficiently solvable.

The second paper, The Weisfeiler-Leman Dimension of Existential Conjunctive Queries by Andreas Göbel with researchers from Oxford was published at the PODS International Conference on Management of Data, which takes place on 9-14 June in Santiago, Chile. In this paper, the authors determine the Weisfeler-Leman dimension of counting conjunctive queries to a graph. Given a conjunctive query they show that its WL-dimension is equal to the semantic extension width, a novel width measure that can be thought of as a combination of the treewidth and the quantified star size of the query.

  • Constantinescu, Andrei; Lenzner, Pascal; Reiffenhäuser, Rebecca; Schmand, Daniel; Varricchio, Giovanna Solving Woeginger’s Hiking Problem: Wonderful Partitions in Anonymous Hedonic GamesInternational Colloquium on Automata, Languages and Programming (ICALP) 2024