Algorithms for the treewidth and minimum fill-in of HHD-free graphs

A graph is HHD-free is it does not contain a house (i.e., the complement of P 5), a hole (a cycle of length at least 5) or a domino (the graph obtained from two 4-cycles by identifying an edge in one C 4 with an edge in the other C 4) as an induced subgraph. The minimum fill-in problem is the problem of finding a chordal supergraph with the smallest possible number of edges. The treewidth problem is the problem of finding a chordal embedding of the graph with the smallest possible clique number. In this note we show that both problems are solvable in polynomial time for HHD-free graphs