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Random kk-out subgraph leaves only O(n/k)O(n/k) inter-component edges

IEEE Annual Symposium on Foundations of Computer Science (FOCS), 2019
Abstract

Each vertex of an arbitrary simple graph on nn vertices chooses kk random incident edges. What is the expected number of edges in the original graph that connect different connected components of the sampled subgraph? We prove that the answer is O(n/k)O(n/k), when kclognk\ge c\log n, for some large enough cc. We conjecture that the same holds for smaller values of kk, possibly for any k2k\ge 2. Such a result is best possible for any k2k\ge 2. As an application, we use this sampling result to obtain a one-way communication protocol with \emph{private} randomness for finding a spanning forest of a graph in which each vertex sends only O(nlogn){O}(\sqrt{n}\log n) bits to a referee.

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