• Media type: Electronic Conference Proceeding; Text; E-Article
  • Title: Fixed-Parameter Algorithms for Longest Heapable Subsequence and Maximum Binary Tree
  • Contributor: Chandrasekaran, Karthekeyan [Author]; Grigorescu, Elena [Author]; Istrate, Gabriel [Author]; Kulkarni, Shubhang [Author]; Lin, Young-San [Author]; Zhu, Minshen [Author]
  • imprint: Schloss Dagstuhl – Leibniz-Zentrum für Informatik, 2020
  • Language: English
  • DOI: https://doi.org/10.4230/LIPIcs.IPEC.2020.7
  • Keywords: maximum binary tree ; permutation directed acyclic graphs ; heapability
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  • Description: A heapable sequence is a sequence of numbers that can be arranged in a min-heap data structure. Finding a longest heapable subsequence of a given sequence was proposed by Byers, Heeringa, Mitzenmacher, and Zervas (ANALCO 2011) as a generalization of the well-studied longest increasing subsequence problem and its complexity still remains open. An equivalent formulation of the longest heapable subsequence problem is that of finding a maximum-sized binary tree in a given permutation directed acyclic graph (permutation DAG). In this work, we study parameterized algorithms for both longest heapable subsequence and maximum-sized binary tree. We introduce alphabet size as a new parameter in the study of computational problems in permutation DAGs and show that this parameter with respect to a fixed topological ordering admits a complete characterization and a polynomial time algorithm. We believe that this parameter is likely to be useful in the context of optimization problems defined over permutation DAGs.
  • Access State: Open Access