About Sliding Puzzle
The sliding puzzle has been frustrating people since the 1880s, when the original 15 puzzle became a genuine international craze. The rules take one sentence: slide tiles into the single empty space until the numbers are in order. Solving it takes considerably longer.
What makes it hard is that tiles can't be moved independently — every move you make to fix one tile disturbs another. The solution technique is layered: you lock rows and columns from the outside in, and the last 2×2 corner is where beginners lose their runs. Every shuffle here is guaranteed solvable, and boards from 3×3 up to 5×5 are available.
How to play
- Click any tile adjacent to the empty square to slide it into that space.
- You can also use the arrow keys, which slide the tile from that direction into the gap.
- Arrange all tiles in ascending numerical order, with the empty square in the bottom right.
- Every tile slide counts as one move — the goal is to finish in as few as possible.
- Choose 3×3, 4×4 or 5×5. Each board size keeps its own personal best.
Five tips that actually move your score
- Solve top-down, left-to-right. Complete the top row first, then the left column of what's left, then repeat on the smaller remaining square. Never disturb a finished row.
- Learn the last-two-of-a-row trick. The final two tiles of any row cannot be placed one at a time. Put the last tile where the second-to-last belongs, the second-to-last directly beneath it, then rotate them both into place.
- Park the blank deliberately. Before starting a manoeuvre, move the empty square to where the sequence needs it. Most wasted moves come from bringing the blank around the long way.
- Count in cycles, not in tiles. Moving a tile one square usually costs a five-move loop of the blank. Thinking in loops makes the move count predictable.
- On 5×5, be patient. Optimal solutions exceed a hundred moves. Rushing produces exactly the tangle the layered method is designed to avoid.
Frequently asked questions
Are all shuffles solvable?
Yes. The board is scrambled by making legal random moves from the solved state, which guarantees a solution always exists.
What is the minimum number of moves for a 4×4?
The hardest possible 15-puzzle position needs 80 moves. A typical random shuffle can usually be solved in 40 to 60 with good technique.
Why can I not just swap the last two tiles?
Because half of all tile arrangements are mathematically unreachable. A single swap flips the board into the unsolvable parity class, which is why the rotation trick is necessary.
Is there a timer?
The move count is the score here, so you can take as long as you like on any single move.