A faster algorithm for the $k$-forest problem: breaking the $O_k(n^{3/2})$ complexity barrier

The $k$-forest problem asks to find $k$ forests in a graph $G$ maximizing the number of edges in their union. We show how to solve this problem in $O(k^3 \min\{kn, m\} \log^2 n + k \cdot{\rm MAXFLOW}(m, m) \log n)$ time, breaking the $O_k(n^{3/2})$ complexity barrier of previously known approaches. Our algorithm relies on three subroutines: the directed $k$-forest problem with bounded indegree condition, the $k$-pseudoforest problem, and the top clump computation.