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Free, publicly-accessible full text available December 31, 2025
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Abstract In 2003, Bohman, Frieze, and Martin initiated the study of randomly perturbed graphs and digraphs. For digraphs, they showed that for every$$\alpha \gt 0$$, there exists a constant$$C$$such that for every$$n$$-vertex digraph of minimum semi-degree at least$$\alpha n$$, if one adds$$Cn$$random edges then asymptotically almost surely the resulting digraph contains a consistently oriented Hamilton cycle. We generalize their result, showing that the hypothesis of this theorem actually asymptotically almost surely ensures the existence of every orientation of a cycle of every possible length, simultaneously. Moreover, we prove that we can relax the minimum semi-degree condition to a minimum total degree condition when considering orientations of a cycle that do not contain a large number of vertices of indegree$$1$$. Our proofs make use of a variant of an absorbing method of Montgomery.more » « less
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null (Ed.)Abstract A perfect K r -tiling in a graph G is a collection of vertex-disjoint copies of the clique K r in G covering every vertex of G . The famous Hajnal–Szemerédi theorem determines the minimum degree threshold for forcing a perfect K r -tiling in a graph G . The notion of discrepancy appears in many branches of mathematics. In the graph setting, one assigns the edges of a graph G labels from {‒1, 1}, and one seeks substructures F of G that have ‘high’ discrepancy ( i.e. the sum of the labels of the edges in F is far from 0). In this paper we determine the minimum degree threshold for a graph to contain a perfect K r -tiling of high discrepancy.more » « less
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