The n-Puzzle is a sliding puzzle that consists of a frame of numbered square pieces in random order with one piece missed. If the size is 3×3 pieces, the puzzle is called the 8-puzzle or 9-puzzle, and if 4×4 tiles, the puzzle is called the 15-puzzle or 16-puzzle named, respectively, for the number of pieces and the number of spaces. The object of the puzzle is to place the pieces in order by making sliding moves that use the empty space.