The board has one empty square. Slide any tile next to the gap into it, one move at a time, until the tiles read 1, 2, 3 … in order from the top left, with the gap in the bottom-right corner. In picture mode the finished board shows the whole picture.
The 4×4 version with 15 tiles became a worldwide craze in the 1880s. Only half of all possible arrangements can ever be solved — the solver explains the neat counting rule (inversions) that tells you which half a position is in.
A good way to work by hand: finish the top row, then the left column, and keep shrinking the puzzle until a 2×2 corner is left.
Slide tiles into the empty square, one at a time, until they are back in order with the gap at the bottom right.
The full guide, with a worked example and common mistakes: How to play Sliding Tiles.
Each slide changes the number of inversions in a fixed way, so a hidden ‘odd or even’ value never changes. Positions with the wrong value can never reach the finished board.
Yes — the hint and the solver search for the fewest moves. For very scrambled 4×4 positions the solver may give a short solution instead if the exact search runs out of time, and says so.
Yes — download a PDF of puzzles with the shortest solutions at the back. Sliding puzzles don’t work on the Slate whiteboard, so there’s no Slate file for this one.
Open the Sliding Tiles Solver, set up your position and press Solve.