Let \(r(a)\) be the replication number of the vertex \(a\) of a path design \(P(v,k, 1)\), \(k \geq 3\). Let \(\bar{r}(v,k) = \text{min}\{\text{max}_{a\in V} \,r(a) | (V,\mathcal{B}) \text{ is a } P(v,k, 1)\}\). A path design \(P(v,k,1)\), \((W,\mathcal{D})\), is said to be \({almost\; balanced}\) if \(\bar{r}(v,k) – 1 \leq r(y) \leq \bar{r}(v,k)\) for each \(y \in W\). Let \(v \equiv 0 \text{ or } 1 \pmod{2(k-1)}\) (for each odd \(k\), \(k \geq 3\)) and let \(v_y \equiv 0 \text{ or } 1 \pmod{k-1}\) (for each even \(k\), \(k \geq 4\)). In this note, we determine the spectrum \(\mathcal{B}\mathcal{S}\mathcal{A}\mathcal{B}\mathcal{P}(v,k,1)\) of integers \(x\) such that there exists an almost balanced path design \(P(v,k, 1)\) with a blocking set of cardinality \(x\).

A border of a string \(x\) is a proper (but possibly empty) prefix of \(x\) that is also a suffix of \(x\). The \({border \;array}\) \(\beta = \beta[1..n]\) of a string \(x = x[1..n]\) is an array of nonnegative integers in which each element \(\beta(i)\), \(1 \leq i \leq n\), is the length of the longest border of \(x[1..i]\). In this paper, we first present a simple linear-time algorithm to determine whether or not a given array \(y = y[1..n]\) of integers is a border array of some string on an alphabet of unbounded size, and then a slightly more complex linear-time algorithm for an alphabet of any given (bounded) size \(\alpha\). We then consider the problem of generating all possible distinct border arrays of given length \(n\) on a bounded or unbounded alphabet, and doing so in time proportional to the number of arrays generated. A previously published algorithm that claims to solve this problem in constant time per array generated is shown to be incorrect, and new algorithms are proposed. We conclude with an equally efficient on-line algorithm for this problem.

In developing an observation made by the author concerning a class of expansions of the sine function, M. Xinrong has recently analysed the question of a generalised form through a succinct use of linear operator theory. This paper constitutes an extension of his work, in which the current problem is solved completely by examining the generating function of a finite sequence central to the formulation.

For graphs \(G\) and \(H\), the Ramsey number \(R(G, H)\) is the least integer \(n\) such that every 2-coloring of the edges of \(K_n\) contains a subgraph isomorphic to \(G\) in the first color or a subgraph isomorphic to \(H\) in the second color. Graph \(G\) is a \((C_4, K_n)\)-graph if \(G\) doesn’t contain a cycle \(C_4\) and \(G\) has no independent set of order \(n\). Jayawardene and Rousseau showed that \(21 \leq R(C_4, K_7) \leq 22\). In this work, we determine \(R(C_4, K_7) = 22\) and \(R(C_4, K_8) = 26\), and enumerate various families of \((C_4, K_n)\)-graphs. In particular, we construct all \((C_4, K_n)\)-graphs for \(n < 7\), and all \((C_4, K_n)\)-graphs on at least 19 vertices. Most of the results are based on computer algorithms.