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Improved FPT Algorithms for Deletion to Forest-Like Structures

  • Kishen N. Gowda,
  • Aditya Lonkar,
  • Fahad Panolan,
  • Vraj Patel,
  • Saket Saurabh

摘要

The Feedback Vertex Set problem is undoubtedly one of the most well-studied problems in Parameterized Complexity. In this problem, given an undirected graph G and a non-negative integer k, the objective is to test whether there exists a subset \(S\subseteq V(G)\) S V ( G ) of size at most k such that \(G-S\) G - S is a forest. After a long line of improvement, recently, Li and Nederlof [TALG, 2022] designed a randomized algorithm for the problem running in time \({\mathcal {O}}^{\star }(2.7^k)^{*}\) O ( 2 . 7 k ) . In the Parameterized Complexity literature, several problems around Feedback Vertex Set have been studied. Some of these include Independent Feedback Vertex Set (where the set S should be an independent set in G), Almost Forest Deletion and Pseudoforest Deletion. In Pseudoforest Deletion, each connected component in \(G-S\) G - S has at most one cycle in it. However, in Almost Forest Deletion, the input is a graph G and non-negative integers \(k,\ell \in {{\mathbb {N}}}\) k , N , and the objective is to test whether there exists a vertex subset S of size at most k, such that \(G-S\) G - S is \(\ell \) edges away from a forest. In this paper, using the methodology of Li and Nederlof [TALG, 2022], we obtain the current fastest algorithms for all these problems. In particular we obtain the following randomized algorithms. 1.

Independent Feedback Vertex Set can be solved in time \({\mathcal {O}}^{\star }(2.7^k)\) O ( 2 . 7 k ) .

2.

Pseudo Forest Deletion can be solved in time \({\mathcal {O}}^{\star }(2.85^k)\) O ( 2 . 85 k ) .

3.

Almost Forest Deletion can be solved in time \({\mathcal {O}}^{\star }(\min \{2.85^k \cdot 8.54^\ell ,2.7^k \cdot 36.61^\ell ,3^k \cdot 1.78^\ell \})\) O ( min { 2 . 85 k · 8 . 54 , 2 . 7 k · 36 . 61 , 3 k · 1 . 78 } ) .