Given a vector ( 1 2 ::: t) of non increasing positive integers, and an undirected graph G = (V E), an L( 1 2 ::: t)-coloring of G is a function f from the vertex set V to a set of nonnegative integerssuch that jf(u) ; f(v)j i, if d(u v) = i 1 i t where d(u v) is the distance (i.e. the minimum number of edges) between the vertices u and v. This paper presents e cient algorithms for nding optimal L(1 ::: 1)-colorings of trees and interval graphs. Moreover, e cient algorithms are also provided for nding approximate L( 1 1 ::: 1)-colorings of trees and interval graphs, as well as appr oximateL( 1 2)colorings of unit interval graphs.
Alan A. Bertossi, Maria Cristina Pinotti, Romeo Ri