A linear time algorithm for L(2,1)-labeling of trees

Toru Hasunuma Toshimasa Ishii Hirotaka Ono Yushi Uno A linear time algorithm for L(2,1)-labeling of trees http://arxiv.org/abs/0810.0906 2008 CoRR abs/0810.0906 db/journals/corr/corr0810.html#abs-0810-0906 informal publication