Phased State Space Search

PS*, a new sequential tree searching algorithm based on the State Space Search (SSS*), is presented. PS*(k) divides each MAX node of a game tree into k partitions, which are then searched in sequence. By this means two major disadvantages of SSS*, storage demand and maintenance overhead, are significantly reduced, and yet the corresponding increase in nodes visited is not so great even in the random tree case. The performance and requirements of PS* are compared on both theoretical and experimental grounds to the well known αβ and SSS* algorithms. The basis of the comparison is the storage needs and the average count of the bottom positions visited. To appear in the Procs. of the ACM/IEEE Fall Joint Computer Conference, Dallas, Nov. 1986.