Bidirectional search that is guaranteed to meet in the middle

Abstract

We present MM, the first bidirectional heuristic search algorithm whose forward and backward searches are guaranteed to "meet in the middle", i.e. never expand a node beyond the solution midpoint. We also present a novel framework for comparing MM, A∗, and brute-force search, and identify conditions favoring each algorithm. Finally, we present experimental results that support our theoretical analysis.