  We present a new algorithm A*+BFHS for solving problems with unit-cost
operators where A* and IDA* fail due to memory limitations and/or the existence
of many distinct paths between the same pair of nodes. A*+BFHS is based on A*
and breadth-first heuristic search (BFHS). A*+BFHS combines advantages from
both algorithms, namely A*'s node ordering, BFHS's memory savings, and both
algorithms' duplicate detection. On easy problems, A*+BFHS behaves the same as
A*. On hard problems, it is slower than A* but saves a large amount of memory.
Compared to BFIDA*, A*+BFHS reduces the search time and/or memory requirement
by several times on a variety of planning domains.
