Fifteen (Number Puzzle)

The Fifteen (15-puzzle), also called Gem Puzzle, Boss Puzzle, Game of Fifteen, Mystic Square and many others - is a sliding puzzle that consists of a frame of numbered square tiles in random order with one tile missing. The puzzle, if 4×4 tiles, the puzzle is called the 15-puzzle or 16-puzzle named, respectively, for the number of tiles and the number of spaces.