Deadline-Aware Search Using On-Line Measures of Behavior

In many applications of heuristic search, insufficient time is available to find provably optimal solutions. We consider the contract search problem: finding the best solution possible within a given time limit. The conventional approach to this problem is to use an interruptible anytime algorithm. Such algorithms return a sequence of improving solutions until interuppted and do not consider the approaching deadline during the course of the search. We propose a new approach, Deadline Aware Search, that explicitly takes the deadline into account and attempts to use all available time to find a single high-quality solution. This algorithm is simple and fully general: it modifies best-first search with on-line pruning. Empirical results on variants of gridworld navigation, the sliding tile puzzle, and dynamic robot navigation show that our method can surpass the leading anytime algorithms across a wide variety of deadlines.