Circular Digraph Walks, k-Balanced Strings, Lattice Paths and Chebychev   Polynomials
  We count the number of walks of length n on a k-node circular digraph that cover all k nodes in two ways. The first way illustrates the transfer-matrix method. The second involves counting various classes of height-restricted lattice paths. We observe that the results also count so-called k-balanced strings of length n, generalizing a 1996 Putnam problem. 
Evangelos Georgiadis, David Callan, Qing-Hu Hou