Efficient Randomized Distributed Coloring in CONGEST
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Distributed vertex coloring is one of the classic problems and probably also the most widely studied problems in the area of distributed graph algorithms. We present a new randomized distributed vertex coloring algorithm for the standard CONGEST model, where the network is modeled as an n-node graph G, and where the nodes of G operate in synchronous communication rounds in which they can exchange O(log n)-bit messages over all the edges of G. For graphs with maximum degree Δ, we show that the (Δ+1)-list coloring problem (and therefore also the standard (Δ+1)-coloring problem) can be solved in O(log^5log n) rounds. Previously such a result was only known for the significantly more powerful LOCAL model, where in each round, neighboring nodes can exchange messages of arbitrary size. The best previous (Δ+1)-coloring algorithm in the CONGEST model had a running time of O(logΔ + log^6log n) rounds. As a function of n alone, the best previous algorithm therefore had a round complexity of O(log n), which is a bound that can also be achieved by a naïve folklore algorithm. For large maximum degree Δ, our algorithm hence is an exponential improvement over the previous state of the art.
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