AI: About the 8 or 15 Puzzle
The 8 Puzzle consists of a 3x3 board with eight numbered tiles and an empty spot. A tile adjacent to the empty spot can slide into that spot. The goal of the puzzle is to order all of the tiles numerically, leaving the empty spot in the lower-right corner. The 15 Puzzle is the same puzzle only with 15 tiles on a 4x4 board.