Customizable Contraction Hierarchies

Abstract

We consider the problem of quickly computing shortest paths in weighted graphs. Often, this is achieved in two phases: (1) derive auxiliary data in an expensive preprocessing phase, and (2) use this auxiliary data to speed up the query phase. By adding a fast weight-customization phase, we extend Contraction Hierarchies to support a three-phase workflow. The expensive preprocessing is split into a phase exploiting solely the unweighted topology of the graph and a lightweight phase that adapts the auxiliary data to a specific weight. We achieve this by basing our Customizable Contraction Hierarchies (CCHs) on nested dissection orders. We provide an in-depth experimental analysis on large road and game maps showing that CCHs are a very practicable solution in scenarios where edge weights often change.