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Algorithmic Aspects of Partial List Colourings

Published online by Cambridge University Press:  03 November 2000

M. VOIGT
Affiliation:
Institut für Mathematik, Technische Universität Ilmenau, PF0565, D-98684 Ilmenau, Germany (e-mail: voigt@mathematik.tu-ilmenau.de)

Abstract

Let G = (V, E) be a graph with n vertices, chromatic number χ(G) and list chromatic number χ[lscr ](G). Suppose each vertex of V(G) is assigned a list of t colours. Albertson, Grossman and Haas [1] conjectured that at least [formula here] vertices can be coloured properly from these lists.

Albertson, Grossman and Haas [1] and Chappell [3] proved partial results concerning this conjecture. This paper presents algorithms that colour at least the number of vertices given in the bounds of Albertson, Grossman and Haas, and Chappell. In particular, it follows that the conjecture is valid for all bipartite graphs and that, for every bipartite graph and every assignment of lists with t colours in each list where 0 [les ] t [les ] χ[lscr ](G), it is possible to colour at least (1 − (1/2)t)n vertices in polynomial time. Thus, if G is bipartite and [Lscr ] is a list assignment with [mid ]L(v)[mid ] [ges ] log2n for all vV, then G is [Lscr ]-list colourable in polynomial time.

Type
Research Article
Copyright
2000 Cambridge University Press

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