DeepAI

# Twin-width III: Max Independent Set and Coloring

We recently introduced the graph invariant twin-width, and showed that first-order model checking can be solved in time f(d,k)n for n-vertex graphs given with a witness that the twin-width is at most d, called d-contraction sequence or d-sequence, and formulas of size k [Bonnet et al., FOCS '20]. The inevitable price to pay for such a general result is that f is a tower of exponentials of height roughly k. In this paper, we show that algorithms based on twin-width need not be impractical. We present 2^O(k)n-time algorithms for k-Independent Set, r-Scattered Set, k-Clique, and k-Dominating Set when an O(1)-sequence is provided. We further show how to solve weighted k-Independent Set, Subgraph Isomorphism, and Induced Subgraph Isomorphism, in time 2^O(k log k)n. These algorithms are based on a dynamic programming scheme following the sequence of contractions forward. We then show a second algorithmic use of the contraction sequence, by starting at its end and rewinding it. As an example of this reverse scheme, we present a polynomial-time algorithm that properly colors the vertices of a graph with relatively few colors, establishing that bounded twin-width classes are χ-bounded. This significantly extends the χ-boundedness of bounded rank-width classes, and does so with a very concise proof. The third algorithmic use of twin-width builds on the second one. Playing the contraction sequence backward, we show that bounded twin-width graphs can be edge-partitioned into a linear number of bicliques, such that both sides of the bicliques are on consecutive vertices, in a fixed vertex ordering. Given that biclique edge-partition, we show how to solve the unweighted Single-Source Shortest Paths and hence All-Pairs Shortest Paths in sublinear time O(n log n) and time O(n^2 log n), respectively.

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04/30/2020

### Twin-width I: tractable FO model checking

Inspired by a width invariant defined on permutations by Guillemot and M...
10/30/2021

### Twin-width VI: the lens of contraction sequences

A contraction sequence of a graph consists of iteratively merging two of...
07/04/2023

### Sparse Graphs of Twin-width 2 Have Bounded Tree-width

Twin-width is a structural width parameter introduced by Bonnet, Kim, Th...
06/17/2020

### Twin-width II: small classes

The twin-width of a graph G is the minimum integer d such that G has a d...
07/15/2022

### Approximating Highly Inapproximable Problems on Graphs of Bounded Twin-Width

For any ε > 0, we give a polynomial-time n^ε-approximation algorithm for...
05/30/2022

### On algorithmic applications of sim-width and mim-width of (H_1, H_2)-free graphs

Mim-width and sim-width are among the most powerful graph width paramete...
11/06/2018

### Finding Independent Transversals Efficiently

We give an efficient algorithm that, given a graph G and a partition V_1...