Challenges for AI Research
•The 15 Puzzle is a version of the Sliding Tile Puzzle, which is an important test domain for heuristic search.
•A heuristic is an estimation of the distance remaining from the current position in the game to the goal.
•A state is a possible configuration of the tiles in the puzzle.
•There are 16! possible configurations of the tiles in the 15 Puzzle. Half of these configurations are not solvable, and it is easy to tell whether or not a configuration can be solved. Even with 16!/2 remaining configurations that can be solved, there are still far more states than can be stored in memory in a computer.
•Search algorithms look for the shortest (optimal) path of moves from the current state of the game to the goal.
•A* finds the shortest possible path, but even on the 15 Puzzle, it is impossible to store all the states of the game in memory. Therefore, other variations of A* must be used to reduce memory requirements. An example is IDA*, which uses a technique called iterative-deepening.
•Current techniques can find the shortest possible path in the 15 Puzzle, but larger versions of the sliding tile puzzle is still difficult.