A general exhaustive generation algorithm for Gray structures

Abstract

Starting from a succession rule for Catalan numbers, we define a procedure for encoding and listing the objects enumerated by these numbers such that two consecutive codes of the list differ only by one digit. The Gray code we obtain can be generalized to all the succession rules with the stability property: each label (k) has in its productions two labels c 1 and c 2, always in the same position, regardless of k. Because of this link, we define Gray structures as the sets of those combinatorial objects whose construction can be encoded by a succession rule with the stability property. This property is a characteristic that can be found among various succession rules, such as the finite, factorial or transcendental ones. We also indicate an algorithm which is a very slight modification of Walsh’s one, working in O(1) worst-case time per word for generating Gray codes.