L(2,1) coloring

L(2, 1)-coloring is a particular case of L(h, k)-coloring which is in fact a proper coloring. In L(2, 1)-coloring of a graph, G, the vertices of the graph G is colored or labelled in such a way that the adjacent vertices get labels that differ by at least two. Also the vertices that are at a distance of two from each other get labels that differ by at least one.