Finding a Heaviest Vertex-Weighted Triangle Is not Harder than Matrix Multiplication

Abstract

We show that a maximum-weight triangle in an undirected graph with n vertices and real weights assigned to vertices can be found in time $\mathcal{O}(n^{\omega}+n^{2+o(1)})$, where $\omega$ is the exponent of the fastest matrix multiplication algorithm. By the currently best bound on $\omega$, the running time of our algorithm is $\mathcal{O}(n^{2.376})$. Our algorithm substantially improves the previous time-bounds for this problem, and its asymptotic time complexity matches that of the fastest known algorithm for finding any triangle (not necessarily a maximum-weight one) in a graph. We can extend our algorithm to improve the upper bounds on finding a maximum-weight triangle in a sparse graph and on finding a maximum-weight subgraph isomorphic to a fixed graph. We can find a maximum-weight triangle in a vertex-weighted graph with m edges in asymptotic time required by the fastest algorithm for finding any triangle in a graph with m edges, i.e., in time $\mathcal{O}(m^{1.41})$. Our algorithms for a maximum-weight fixed subgraph (in particular any clique of constant size) are asymptotically as fast as the fastest known algorithms for a fixed subgraph.