Partitioning a Weighted Graph to Connected Subgraphs of Almost Uniform Size

Abstract

Assume that each vertex of a graph G is assigned a nonnegative integer weight and that l and u are nonnegative integers. One wish to partition G into connected components by deleting edges from G so that the total weight of each component is at least l and at most u. Such an “almost uniform” partition is called an $(l, u) \mbox{-}$partition. We deal with three problems to find an $(l, u) \mbox{-}$partition of a given graph. The minimum partition problem is to find an $(l, u) \mbox{-}$partition with the minimum number of components. The maximum partition problem is defined similarly. The p-partition problem is to find an $(l, u) \mbox{-}$partition with a fixed number p of components. All these problems are NP-complete or NP-hard even for series-parallel graphs. In this paper we show that both the minimum partition problem and the maximum partition problem can be solved in time O(u ⁴ n) and the p-partition problem can be solved in time O(p ² u ⁴ n) for any series-parallel graph of n vertices. The algorithms can be easily extended for partial k-trees, that is, graphs with bounded tree-width.