Cardinality constrained connected balanced partitions of trees under different criteria

Abstract

In this paper we study the problem of partitioning a tree with $n$ weighted vertices into $p$ connected components. For each component, we measure its gap, that is, the difference between the maximum and the minimum weight of its vertices, with the aim of minimizing the sum of such differences. We present an $O\left(n^3{p}^2\right)$ time and $O\left(n^{3}p\right)$ space algorithm for this problem. Then, we generalize it, requiring a minimum of $ϵ\ge 1$ nodes in each connected component, and provide an $O\left(n^3{p}^2{ϵ}^2\right)$ time and $O\left(n^{3}pϵ\right)$ space algorithm to solve this new problem version. We provide a refinement of our analysis involving the topology of the tree and an improvement of the algorithms for the special case in which the weights of the vertices have a heap structure. All presented algorithms can be straightforwardly extended to other similar objective functions. Actually, for the problem of minimizing the maximum gap with a minimum number of nodes in each component, we propose an algorithm which is independent of $ϵ$ and requires $O(n^{2}logn{p}^2)$ time and $O\left(n^{2}p\right)$ space.