Searcharxiv⌕ Search

arXiv subjects

Colm Ó Dúnlaing

Publications and source records attributed to Colm Ó Dúnlaing.

3 recordsLinked to original sources

A coefficient related to splay-to-root traversal, correct to thousands of decimal places

This paper takes another look at the cost of traversing a binary tree using repeated splay-to-root. This was shown to cost $O(n)$ (in rotations) by Tarjan and later, in different ways, by Elmasry and others. It would be interesting to know the minimal possible coefficient implied by the $O(n)$ cost; call this coefficient $β$. In this paper we define a related coefficient $α$ describing the cost of splay-to-root traversal on maximal (i.e., complete) binary trees, and show that $β\geq 2 + α$. We give the first 3009 digits of $α$, including the decimal point, and show that every digit is correct. We make two conjectures: first, that $β= 2 + α$, and second, that $α$ is irrational.

math.CO↗

Compact families of Jordan curves and convex hulls in three dimensions

We prove that for certain families of semi-algebraic convex bodies in 3 dimensions, the convex hull of $n$ disjoint bodies has $O(nλ_s(n))$ features, where $s$ is a constant depending on the family: $λ_s(n)$ is the maximum length of order-$s$ Davenport-Schinzel sequences with $n$ letters. The argument is based on an apparently new idea of `compact families' of convex bodies or discs, and of `crossing content' of disc intersections.

cs.CG↗

An ACCL which is not a CRCL

It is fairly easy to show that every regular set is an almost-confluent congruential language (ACCL), and it is known that every regular set is a Church-Rosser congruential language (CRCL). Whether there exists an ACCL, which is not a CRCL, seems to remain an open question. In this note we present one such ACCL.

cs.LO↗