A Spectral Technique for Coloring Random 3-Colorable Graphs

Noga Alon, Nabil Kahale
1997 SIAM journal on computing (Print)  
Let G 3n,p,3 be a random 3-colorable graph on a set of 3n vertices generated as follows. First, split the vertices arbitrarily into three equal color classes and then choose every pair of vertices of distinct color classes, randomly and independently, to be an edge with probability p. We describe a polynomial time algorithm that finds a proper 3-coloring of G 3n,p,3 with high probability, whenever p ≥ c/n, where c is a sufficiently large absolute constant. This settles a problem of Blum and
more » ... lem of Blum and Spencer, who asked if one can design an algorithm that works almost surely for p ≥ polylog(n)/n. The algorithm can be extended to produce optimal k-colorings of random k-colorable graphs in a similar model, as well as in various related models. Implementation results show that the algorithm performs very well in practice even for moderate values of c. A preliminary version of this paper appeared in the Proc. of the 26 th ACM STOC, ACM Press (1994), 346-355.
doi:10.1137/s0097539794270248 fatcat:uw6tu3q63bdrzgbxwlkqmdiixi