It is about Bin Packing problem.

In Advanced algorithm complexity problem

Local search 3. Let X denotes your assigned problem. Apply the local search approach on X. (a) Devise a neighborhood function (or possibly local transformation) and analyze it cardinality. (b) Show that the devised local transformation is actually a neighborhood function (i.e. all properties hold for it). (c) For a solution, say a, construct some of its neighborhood solutions according to the devised local transformation