Perfect codes in some products of graphs

A r -perfect code in a graph G = ( V ( G ), E ( G )) is a subset C of V ( G ) for which the balls of radius r centered at the vertices of C form a partition of V ( G ). In this paper, we study the existence of perfect codes in corona product and generalized hierarchical product of graphs where the cardinality of U is equal to one or two. Also, we give some examples as applications of our results.