Sliding Puzzle 4×4

The 4×4 is the original form of the sliding puzzle, fifteen numbered tiles in a box with one space to spare, and the reason it's also called the 15 puzzle. It caused a craze in 1880, when people played it in offices, on trains and in newspapers, and it is still the size most people picture when they hear the name.

It is a big step up from the 3×3. There are more than ten trillion solvable layouts, and the hardest of them needs 80 moves even with perfect play. Nobody plays like that by eye, so the usual way is to break the board down: solve the top row, then the left column, then the second row, and finish the last 3×3 corner as its own small puzzle.

The difficult moment is always the end of a line. When you place the last two tiles of a row, they almost never arrive in the right order, so set them up together: the last tile below its spot, the one before it in the corner, and then slide both in at once. The same trick works for the end of a column, turned on its side.

This page deals New Game shuffles only, at 4×4. They are never ranked, and your games, wins and fewest moves are kept on this device. The Daily Challenge on the main page is a 4×4 as well, the same shuffle for everyone, and it is where the leaderboard lives, so a few games here are good practice for it.

Expect your first solves to take a few hundred moves. Once the row method sticks, a hundred or so is a good game.