On-Line Coloring of H-Free Bipartite Graphs
We present a new on-line algorithm for coloring bipartite graphs. This yields a new upper bound on the on-line chromatic number of bipartite graphs, improving a bound due to Lovász, Saks and Trotter. The algorithm is on-line competitive on various classes of H – free bipartite graphs, in particular P6-free bipartite graphs and P7-free bipartite graphs, i.e., that do not contain an induced path on six, respectively seven vertices. The number of colors used by the on-line algorithm in these particular cases is bounded by roughly twice, respectively roughly eight times the on-line chromatic number. In contrast, it is known that there exists no competitive on-line algorithm to color P6-free (or P7-free) bipartite graphs, i.e., for which the number of colors is bounded by any function only depending on the chromatic number.
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