24 Sliding Puzzle

About 24 Sliding Puzzle

The 24 puzzle: twenty-four blocks on a 5×5 tray. The same method as 4×4 with one more row and column to clear first.

The sliding puzzle is a tray of numbered blocks with one empty space. Slide blocks into the gap, one at a time or a whole row at once, until they read in order from 1 in the top-left corner, with the gap at the end. The classic 4×4 version is the famous 15 puzzle. Every shuffle here can be solved.

Also called: 15 puzzle, 8 puzzle, sliding tiles.

How to play Sliding Puzzle

1. Tap or click a block next to the gap to slide it in. Tap a block further along the same row or column and every block between it and the gap slides together, as one move each.
2. On a touch screen you can also swipe: swipe a block toward the gap, or swipe anywhere to move the block beside the gap in that direction.
3. On a keyboard, the arrow keys (or WASD) slide the block next to the gap in the direction of the arrow: Left moves the block on the gap’s right into it.
4. Put the blocks in order: 1, 2, 3… along the top row, then the next row, with the gap in the bottom-right corner. The blocks are coloured by the row they belong in, so a finished row is one colour.
5. Prefer a picture? Pick one of the pictures under the tray. Each block then shows its piece of the picture; the Numbers button turns the small number badges on or off.
6. Your moves and time are counted from your first slide. Finish to see your result and your best for that size.

Rules

• Only a block in the same row or column as the gap can move, and only toward the gap.
• Each block that slides counts as one move, so sliding a row of three blocks counts three.
• The puzzle is solved when every block is in order and the gap is in the bottom-right corner.
• Shuffles are always solvable. Exactly half of all arrangements can be solved, and the game checks each shuffle with the parity rule before dealing it.
• Best moves and best time are kept separately for 3×3, 4×4 and 5×5.

Sliding Puzzle tips and strategy

• Solve the top row first, then the left column. Once they are done, never touch them again: what’s left is a smaller puzzle of the same kind. On 4×4, after the top row and left column you have a 3×3 left.
• Place the last two blocks of a row together. For the top row of a 4×4, put 3 where 4 belongs, 4 just below it, then slide both into place in one turn of the loop.
• Think in loops. Moving the gap around a 2×2 square rotates three blocks. Most repositioning is a series of these small loops.
• Finish the last two rows column by column. Pair each top block with the one under it (like 9 and 13 on 4×4), then park the pair in place together.
• Fewer moves come from planning: before sliding, work out where the gap needs to go and take the short way round.