Petr Golovach
Complexity of Cops and Robber Game
The Cops and Robbers game was defined independently by
Winkler-Nowakowski and Quilliot in the 1980s and since that time has
been studied intensively. Despite of such a study of the combinatorial
properties of the game, almost no algorithmic results on this game are
known. Perhaps the main algorithmic result known about Cops and Robbers
game is the observation that determining whether the cop number of a
graph on n vertices is at most k can be done by a backtracking algorithm
which runs in time n^O(k) (thus polynomial for fixed k). From the
hardness side, Goldstein and Reingold in 1995 proved that the version of
the Cops and Robbers game on directed graphs is EXPTIME-complete. Also,
they have shown that the version of the game on undirected graphs when
the cops and the robber are given their initial positions is also
EXPTIME-complete. They also conjectured that the game on undirected
graphs is also EXPTIME-complete. However, even NP-hardness of the
problem was proved only in 2008 by Fomin, Golovach and Kratochvil. We
survey the known complexity results about the Cops and Robbers game and
its variants and give a list of open problems.