MM: A bidirectional search algorithm that is guaranteed to meet in the middle Academic Article uri icon

abstract

  • 2017 Elsevier B.V. Bidirectional search algorithms interleave two separate searches, a normal search forward from the start state, and a search backward from the goal. It is well known that adding a heuristic to unidirectional search dramatically reduces the search effort. By contrast, despite decades of research, bidirectional heuristic search has not yet had a major impact. Additionally, no comprehensive theory was ever devised to understand the nature of bidirectional heuristic search. In this paper we aim to close this gap. We first present MM, a novel bidirectional heuristic search algorithm. Unlike previous bidirectional heuristic search algorithms, MM's forward and backward searches are guaranteed to meet in the middle, i.e. never expand a node beyond the solution midpoint. Based on this unique attribute we present a novel framework for comparing MM, A*, and their brute-force variants. We do this by dividing the entire state space into disjoint regions based on their distance from the start and goal. This allows us to perform a comparison of these algorithms on a per region basis and identify conditions favoring each algorithm. Finally, we present experimental results that support our theoretical analysis.

published proceedings

  • Artificial Intelligence

author list (cited authors)

  • Holte, R. C., Felner, A., Sharon, G., Sturtevant, N. R., & Chen, J.

citation count

  • 17

complete list of authors

  • Holte, Robert C||Felner, Ariel||Sharon, Guni||Sturtevant, Nathan R||Chen, Jingwei

publication date

  • January 2017