A Hamiltonian Cycle in the Square of a 2-connected Graph in Linear Time
Stephen Alstrup, Agelos Georgakopoulos, Eva Rotenberg, Carsten Thomassen · Society for Industrial and Applied Mathematics eBooks · 2018
Fleischner's theorem says that the square of every 2-connected graph contains a Hamiltonian cycle. We present a proof resulting in an O(|E|) algorithm for producing a Hamiltonian cycle in the square G2 of a 2-connected graph G = (V, E). The previous best was O(|V|2) by Lau in 1980. More generally, we get an O(|E|) algorithm for producing a Hamiltonian path between any two prescribed vertices, and we get an O(|V|2) algorithm for producing cycles C3, C4, …, C|V| in G2 of lengths 3,4, …, |V|, respectively.