Two New Bijections on Lattice Paths

Glenn Hurlbert1, Vikram Kamatt1
1Department of Mathematics and Statistics Arizona State University Tempe, Arizona 85287-1804

Abstract

Suppose \( 2n \) voters vote sequentially for one of two candidates. For how many such sequences does one candidate have strictly more votes than the other at each stage of the voting? The answer is \( \binom{2n}{n} \) and, while easy enough to prove using generating functions, for example, only three combinatorial proofs exist, due to Kleitman, Gessel, and Callan. In this paper, we present two new bijective proofs.

Keywords: lattice path, bijection, ballot problem