Motivated by an assignment problem arising in MapReduce computations, we investigate a generalization of the Bin Packing problem which we call Bin Packing with Colocations Problem. We are given a weigthed graph G = (V,E), where V represents the set of items with positive integer weights and E the set of related (to be colocated) items, and an integer q. The goal is to pack the items into a minimum number of bins so that (i) for each bin, the total weight of the items packed in this bin is at most q, and (ii) for each edge (i,j) ∈ E there is at least one bin containing both items i and j. We first point out that, when the graph is unweighted (i.e., all the items have equal weights), the problem is equivalent to the q-clique problem, and when furthermore the graph is a clique, optimal solutions are obtained from Covering Designs. We prove that the problem is strongly NP-hard even for paths and unweighted trees. Then, we propose approximation algorithms for particular families of graphs, including: a (3+√5)-approximation algorithm for complete graphs (improving a previous ratio of 8), a 2-approximation algorithm for paths, a 5-approximation algorithm for trees, and an (1 + O(log q/q))-approximation algorithm for unweighted trees. For general graphs, we propose a 3 + 2[mad(G)/2]-approximation algorithm, where mad(G) is the maximum average degree of G. Finally, we show how to convert any approximation algorithm for Bin Packing (resp. Densest q-Subgraph) problem into an approximation algorithm for the problem on weighted (resp. unweighted) general graphs.
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