Incremental topological sort and cycle detection in Õ (m √n) expected total time

In the incremental cycle detection problem edges are inserted to a directed graph (initially empty) and the algorithm has to report once a directed cycle is formed in the graph. A closely related problem to the incremental cycle detection is that of the incremental topological sort problem, in which edges are inserted to an acyclic graph and the algorithm has to maintain a valid topological sort on the vertices at all times. Both incremental cycle detection and incremental topological sort have a long history. The state of the art is a recent breakthrough of Bender, Fineman, Gilbert and Tarjan [TALG 2016], with two different algorithms with respective total update times of Õ (n2) and O(m minfm1=2; n2=3g). The two algorithms work for both incremental cycle detection and incremental topological sort. In this paper we introduce a novel technique that allows us to improve upon the state of the art for a wide range of graph sparsity. Our algorithms has a total expected update time of Õ(m p n) for both the incremental cycle detection and the topological sort problems.