Journal of the ACM (JACM)
Nonrepetitive colorings of graphs
Random Structures & Algorithms - Special issue: Proceedings of the tenth international conference "Random structures and algorithms"
Pattern avoidance: themes and variations
Theoretical Computer Science - Combinatorics on words
Applied Combinatorics on Words (Encyclopedia of Mathematics and its Applications)
Applied Combinatorics on Words (Encyclopedia of Mathematics and its Applications)
Parameterized Complexity Theory (Texts in Theoretical Computer Science. An EATCS Series)
Parameterized Complexity Theory (Texts in Theoretical Computer Science. An EATCS Series)
New Constructive Aspects of the Lovász Local Lemma
Journal of the ACM (JACM)
Characterisations and examples of graph classes with bounded expansion
European Journal of Combinatorics
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A coloring of a graph is nonrepetitive if the graph contains no path that has a color pattern of the form xx (where x is a sequence of colors). We show that determining whether a particular coloring of a graph is nonrepetitive is coNP-hard, even if the number of colors is limited to four. The problem becomes fixed-parameter tractable, if we only exclude colorings xx up to a fixed length k of x.