We consider a natural family of motion planning problems with movable obstacles and obtain hardness results for them. Some members of the family are shown to be PSPACE-complete thus improving and extending (and also simplifying) a previous NP-hardness result of Wilfong. The family considered includes a motion planning problem which forms the basis of a popular computer game called SOKOBAN. The ...

This work considers a family of motion planning problems with movable blocks. Such problem is defined by a maze grid occupied by immovable blocks (walls) and free squares. There are k movable blocks (stones) and k fixed goal squares. The man is a movable block that can traverse free squares and move stones between them. The problem goal is to move the stones from their initial positions to the ...

Humans can eeectively navigate through large search spaces, enabling them to solve problems with daunting complexity. This is largely due to an ability to successfully distinguish between relevant and irrelevant actions (moves). In this paper we present a new single-agent search pruning technique that is based on a move's innuence. The innuence measure is a crude form of relevance in that it is...

Sokoban is a game on an integer grid, where a warehouse keeper, or robot, has to push boxes to designated storage locations. He can push a box one cell horizontally or vertically if the destination cell is free. Some of the grid cells can be occupied by unmovable obstacles. Several variants of Sokoban have been studied. In these variants all obstacles may be movable, the keeper may push up to k...

Single-agent search is a powerful tool for solving a variety of applications. Most of the academic application domains used to explore single-agent search techniques have the property that if you start with a solvable state, at no time in the search can you reach a state that is unsolvable (it may, however, not be minimal). In this paper we address the implications that arise when states in the...

Pattern databases have been successfully applied to several problems. Their use assumes that the goal state is known, and once the pattern database is built, commonly it can be used by all instances. However, in Sokoban, before solving the puzzle, the goal position of each stone is unknown. Moreover, each Sokoban instance has its own state space search. In this paper we apply pattern databases ...