The classic sliding block puzzle. The 15-puzzle consists of a 4-by-4 grid with tile numbered $1$ to $15$ placed in the grid. The object of this puzzle is to randomly arrange the tiles on the grid, and ...

John Bradley, a senior at Sayre School in Lexington, said he started solving 15 puzzles in the middle school. The puzzles feature sliding tiles numbered 1-15 and the solver has to arrange them ...