“…The direct product G × H of two graphs G = (V G , E G ) and H = (V H , E H ) is the graph such that its vertex set is V G × V H and edge set is composed of {(u 1 , u 2 ), (v 1 , v 2 )} where {u 1 , v 1 } ∈ E G and {u 2 , v 2 } ∈ E H . The L(2, 1)-labeling problem for the Cartesian product [4,11,20,27,29] and the direct product of some families of graphs are studied by [8,11,10,12,17,21,23].…”