Distributed discovery of large near-cliques

Given an undirected graph and 0≤ε≤1, a set of nodes is called an ε -near clique if all but an ε fraction of the pairs of nodes in the set have a link between them. In this paper we present a fast synchronous network algorithm that uses small messages and finds a near-clique. Specifically, we present a constant-time algorithm that finds, with constant probability of success, a linear size ε -near clique if there exists an ε³-near clique of linear size in the graph. The algorithm uses messages of O(log n) bits. The failure probability can be reduced to n ^-Ω(1) by increasing the time complexity by a logarithmic factor, and the algorithm also works if the graph contains a clique of size Ω(n/(log log n) ^α ) for some α in (0,1) . Our approach is based on a new idea of adapting property testing algorithms to the distributed setting.