On the Generation and Enumeration of some Classes of Convex Polyominoes

A. Del Lungo, E. Duchi, A. Frosini, S. Rinaldi


ECO is a method for the recursive generation, and thereby also the enumeration of classes of combinatorial objects. It has already found successful application in recent literature both to the exhaustive generation and to the uniform random generation of various objects classified according to several parameters of interest, as well as to their enumeration.

In this paper we extend this approach to the generation and enumeration of some classes of convex polyominoes. We begin with a review of the ECO method and of the closely related notion of a succession rule.

From this background, we develop the following principal findings: i) ECO constructions for both column-convex and convex polyominoes; ii) translations of these constructions into succession rules; iii) the consequent deduction of the generating functions of column-convex and of convex polyominoes according to their semi-perimeter, first of all analytically by means of the so-called kernel method, and then in a more novel manner by drawing on some ideas of Fedou and Garcia; iv) algorithms for the exhaustive generation of column convex and of convex polyominoes which are based on the ECO constructions of these object and which are shown to run in constant amortized time.