An Optimal Decentralized $(Δ+ 1)$-Coloring Algorithm

Consider the following simple coloring algorithm for a graph on $n$ vertices. Each vertex chooses a color from ${1, \dotsc, \Delta(G) + 1}$ uniformly at random. While there exists a conflicted vertex choose one such vertex uniformly at random and recolor it with a randomly chosen color. This algorithm was introduced by Bhartia et al. [MOBIHOC'16] for channel selection in WIFI-networks. We show that this algorithm always converges to a proper coloring in expected $O(n \log \Delta)$ steps, which is optimal and proves a conjecture of Chakrabarty and Supinski [SOSA'20].