Sokoban

How to play

Walk into a crate to push it. You can only ever push, never pull, and you cannot push two crates at once or push one into a wall. Get every crate onto a target square to finish the level. Because pushing is one way, a crate shoved into a corner is stuck for good, so the puzzle is really about the order you move things in. Undo is unlimited, and the move counter is the score.

Tips

• Look at the targets before you touch anything. Work out which crate is meant for which square first.
• Never push a crate into a corner unless a target is in it. From a corner it can never move again.
• A crate flat against a wall can only slide along that wall. If its target is off the wall, you have lost it.
• Do the crates furthest from the exit first. Finished crates become walls for everything that follows.
• If a level feels impossible, it usually is now. Undo back to before the move that trapped a crate.

A small puzzle with deep roots

Sokoban, whose name means warehouse keeper, was written in Japan in 1981 by Hiroyuki Imabayashi and has been ported to nearly everything with a screen since. It is deceptively simple to describe and genuinely hard to solve: the general problem of deciding whether a Sokoban level can be completed at all is computationally intractable, which is a formal way of saying that no shortcut exists and even computers have to search.

The first four levels are hand made and teach one idea each. The rest were built by reverse play: crates start on their goals and get pulled apart at random, so every candidate is solvable by construction. Tens of thousands of those were then solved optimally and ranked by how many of their pushes go somewhere other than straight to a goal, because a level where every crate walks directly home is a walk, not a puzzle. Every level was checked by a solver before shipping; an earlier hand made one sealed its crates inside a room the player could never reach, and that check is what caught it. Every level you see now has a known solution, and the move counter is the score.

Reading a level

• Corners are death for crates. A crate pushed into a corner with no target there can never move again.
• Walls are almost as bad. A crate against a wall can only slide along it, so if its target is not on that wall, it is lost.
• Plan the order. Crates that are placed become obstacles, so finish the ones deepest in the level first.
• Look for where you need to stand, not just where the crate goes. Every push needs you on the far side of the crate.
• Undo is unlimited. The moment a level feels impossible, it usually is, and the mistake was several moves ago.

Common questions

Is every level solvable?

Yes. Every level was checked by a solver before shipping. One that turned out to be unsolvable was replaced.

Can I pull a crate?

No. Pushing is the only way to move a crate, which is what makes corners permanent.

What is the score?

Moves. Fewer is better, and your best for each level is saved on this device.