How to play
Tap a tile next to the gap to slide it. Put 1 to 8 in order.
About Sliding Number Puzzle
Sliding Number Puzzle is the little plastic tile game from the bottom of a party bag, moved onto your screen. Eight numbered tiles sit in a three by three frame with one empty space. Slide them around until they read 1 to 8 in order, with the gap in the bottom right corner.
How to play
Tap any tile that is directly beside the empty space, above it, below it, or to the left or right, and it slides into the gap. Tiles cannot move diagonally and cannot jump over each other. Tapping a tile that is not next to the gap does nothing.
The finished picture reads 1, 2, 3 across the top row, 4, 5, 6 across the middle and 7, 8 on the bottom with the space at the end. The counter at the top tracks your moves, and when the puzzle is solved it tells you how many you needed. Tap again for a new shuffle.
Every shuffle can be solved. The game mixes the tiles by making a couple of hundred random legal moves from the finished position, so there is always a way back. That is worth knowing, because a sliding puzzle whose tiles are placed at random is impossible exactly half the time.
A method that always works
You do not need to be clever to solve this puzzle. You need to be orderly. Work from the top down and do not disturb what you have finished.
Start with the top row. Bring the 1 to the top left corner. Then bring the 2 next to it. The 3 is the awkward one, because pushing it straight into the corner would knock the 2 out. The trick is to park the 3 below its corner first, move the 2 across into the corner temporarily, and then rotate the pair into place together. You will see the idea after trying it once.
Next, deal with the left column. The 1 is already there, so place the 4 beneath it and then the 7 beneath that, using the same parking trick for the 7.
Now only four squares are left: the positions for 5, 6 and 8, plus the gap. Leave the top row and left column alone and simply move those three tiles round and round in a circle. Within a few turns they drop into order.
Solving it in fewer moves
Once you can finish every time, start watching the counter. It is known that any arrangement of this puzzle can be solved in thirty-one moves or fewer, and most need around twenty. The step-by-step method above is reliable but wasteful, often taking fifty or more.
To do better, look before you slide. Notice tiles that are already close to home and plan to leave them be. Try to move two tiles towards their places with one sequence. And avoid undoing a move you have just made, which is the most common way to burn through the count.
Why it has lasted
Sliding puzzles have been popular since the 1870s, and the appeal has not changed. The rules take ten seconds, there is nothing to memorise, and every solution is something you worked out yourself. It is a good quiet game for children learning to plan ahead and for adults who want five minutes of gentle thinking.
It plays free in your browser on phones, tablets and computers, with nothing to download.