Tree Containment Above Minimum Degree is FPT

Abstract

According to the classic Chv{á}tal's Lemma from 1977, a graph of minimum degree $\delta (G)$ contains every tree on $\delta (G)+1$ vertices. Our main result is the following algorithmic "extension" of Chvátal's Lemma: For any $n$-vertex graph $G$, integer $k$, and a tree $T$ on at most $\delta (G)+k$ vertices, deciding whether $G$ contains a subgraph isomorphic to $T$, can be done in time $f(k)\cdot n^{\mathcal{O}(1)}$ for some function $f$ of $k$ only. The proof of our main result is based on an interplay between extremal graph theory and parameterized algorithms.

Accepted to SODA 2024