BS*: an admissible bidirectional staged heuristic search algorithm

Reviewer: Edward Sava-Segal

In this paper, the author introduces a new member in the class of non-wave-shaping admissible bidirectional algorithms. The algorithm is called BS* and represents an improvement of BHPA [1], the bidirectional version of the celebrated algorithm A* [2]. The author describes four search-reduction operations—nipping, pruning, trimming, and screening—used to accelerate the earlier termination of the search process by removing unfruitful paths in the search graph. He demonstrates that these improvements do not harm the admissibility of BS*. The author reports a full range of experimental results and shows that BS* is the best algorithm in its class in terms of time and space. Kwa also claims that BS* can compute optimal solutions faster than A* by implementing the bidirectional search in parallel. This paper should be of interest to those who want to use the algorithm in a specific environment and those concerned with theoretical issues in the field of heuristic search algorithms. Familiarity with this domain of research is not necessary to understand this well-written paper.