On the Fixed-Parameter Tractability of Capacitated Clustering

We study the complexity of the classic capacitated k-median and k-means problems parameterized by the number of centers, k. These problems are notoriously difficult since the best known approximation bound for high dimensional Euclidean space and general metric space is $Θ(\log k)$ and it remains a major open problem whether a constant factor exists. We show that there exists a $(3+ε)$-approximation algorithm for the capacitated k-median and a $(9+ε)$-approximation algorithm for the capacitated k-means problem in general metric spaces whose running times are $f(ε,k) n^{O(1)}$. For Euclidean inputs of arbitrary dimension, we give a $(1+ε)$-approximation algorithm for both problems with a similar running time. This is a significant improvement over the $(7+ε)$-approximation of Adamczyk et al. for k-median in general metric spaces and the $(69+ε)$-approximation of Xu et al. for Euclidean k-means.