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Conference Papers Year : 2018

Topological Sorting with Regular Constraints


We introduce the constrained topological sorting problem (CTS): given a regular language K and a directed acyclic graph G with labeled vertices, determine if G has a topological sort that forms a word in K. This natural problem applies to several settings, e.g., scheduling with costs or verifying concurrent programs. We consider the problem CTS[K] where the target language K is fixed, and study its complexity depending on K. We show that CTS[K] is tractable when K falls in several language families, e.g., unions of monomials, which can be used for pattern matching. However, we show that CTS[K] is NP-hard for K = (ab) * and introduce a shuffle reduction technique to show hardness for more languages. We also study the special case of the constrained shuffle problem (CSh), where the input graph is a disjoint union of strings, and show that CSh[K] is additionally tractable when K is a group language or a union of district group monomials. We conjecture that a dichotomy should hold on the complexity of CTS[K] or CSh[K] depending on K, and substantiate this by proving a coarser dichotomy under a different problem phrasing which ensures that tractable languages are closed under common operators.
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hal-01950909 , version 1 (11-12-2018)


  • HAL Id : hal-01950909 , version 1


Antoine Amarilli, Charles Paperman. Topological Sorting with Regular Constraints. ICALP 2018 - 45th International Colloquium on Automata, Languages, and Programming, Jul 2018, Prague, Czech Republic. pp.115:1--115:14. ⟨hal-01950909⟩
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