Bidirectional Search That Is Guaranteed to Meet in the Middle

Robert C. Holte, Ariel Felner, Guni Sharon, Nathan R. Sturtevant

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.